Patent Publication Number: US-11378283-B2

Title: Hot water supply device

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the priority benefit of Japan application serial no. 2019-055992, filed on Mar. 25, 2019. The entirety of the above-mentioned patent application is hereby incorporated by reference herein and made a part of this specification. 
     BACKGROUND 
     Technical Field 
     The present disclosure relates to a hot water supply device, and more particularly, to a hot water supply device having an instant hot water function. 
     Description of Related Art 
     As one type of a hot water supply device, there is a device having a so-called instant hot water function in which hot water of an appropriate temperature is output immediately after hot water supply is started even after hot water supply has been turned off for a long time. Normally, in order to realize the instant hot water function, it is necessary to provide a mode for forming a circulation path via a heat source even while hot water supply is stopped (hereinafter, an instant “hot water operation mode”). The instant hot water function can also contribute to water saving by reducing waste water. 
     Japanese Patent Laid-Open No. 2018-136067 (Patent Literature 1) describes a configuration in which an instant hot water circulating unit including a circulation pump is externally mounted on a water heater to realize an instant hot water function. The hot water circulation unit of Patent Literature 1 further includes a cleaning tank for storing a cleaning agent and automatically performs a cleaning operation using the cleaning agent periodically, specifically, after a lapse of a certain time or every time hot water is supplied at a certain flow rate, by operating the circulation pump. Accordingly, it is possible to prevent scale from adhering to the inside of a piping, particularly in a heat exchanger. 
     Patent Literatures 
     [Patent Literature 1] Japanese Patent Laid-Open No. 2018-136067 
     SUMMARY 
     In a hot water supply device with an instant hot water function, when a circulation pump is continuously stopped for a long period of time in the summer, or the like, for example, in areas in which hard water is used as clean water, there is concern of a rotating shaft becoming stuck due to scale adhering around a pump bearing. On the other hand, in an environment in which a circulation pump is operated at a certain frequency, such as in the winter, similar fixation is unlikely to occur. Therefore, as in the cleaning operation of Patent Literature 1, even when the cleaning operation is performed after a lapse of a certain time or every time hot water is supplied at a certain flow rate, it is difficult to efficiently prevent the adhesion of scale. 
     Further, in order to prevent scale adhesion in a circulation pump, it is not necessary to use a cleaning agent, and the amount of time taken by cleaning operations such as that in Patent Literature 1 is not necessary. Therefore, unlike the cleaning operation of Patent Literature 1, a scale adhesion preventing operation of a circulation pump can be easily switched to a hot water supply operation. 
     The disclosure has been made in order to solve such problems, and it is desirable to efficiently and appropriately perform a scale adhesion preventing operation of a circulation pump which is operated in an instant hot water operation. 
     According to an aspect of the disclosure, there is provided a hot water supply device which supplies hot water to a hot water tap, including a heating mechanism, an internal path, and a controller. The internal path forms an instant hot water circulation path through which a fluid passes through the heating mechanism, together with an external path which bypasses the hot water tap outside the hot water supply device when the hot water tap is closed and a circulation pump is operated. The controller instructs operation and stop of the heating mechanism and the circulation pump, wherein the controller performs a protection operation of operating the circulation pump for a second time when a first condition that the stop of the circulation pump have continued for a first time is satisfied and a second condition related to stop of a hot water supply operation is further satisfied. 
     According to the disclosure, it is possible to efficiently and appropriately perform a scale adhesion preventing operation of a circulation pump which is operated in an instant hot water supply operation. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram showing a configuration of a hot water supply system including a hot water supply device according to an embodiment. 
         FIG. 2  is a block diagram showing a configuration example of a controller and related hardware shown in  FIG. 1 . 
         FIG. 3  is a state transition diagram of a protection operation of a circulation pump by the hot water supply device according to Embodiment 1. 
         FIG. 4  is a chart showing a list of content of each condition shown in  FIG. 3 . 
         FIG. 5  is a flowchart showing a control process related to management of a protection operation completion flag shown in  FIG. 3 . 
         FIG. 6  is a waveform diagram showing an operation example of a protection operation of the circulation pump by the hot water supply device according to Embodiment 1. 
         FIG. 7  is a state transition diagram of a protection operation of a circulation pump by a hot water supply device according to Embodiment 2. 
         FIG. 8  is a chart showing a list of content of conditions shown in  FIG. 7 . 
         FIG. 9  is a block diagram showing a configuration of a hot water supply system including a hot water supply device according to a modified example of the embodiment. 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. The same or corresponding parts in the drawings are given the same reference numerals below, and description thereof will not be repeated in principle. 
     Embodiment 1 
       FIG. 1  is a block diagram showing a configuration of a hot water supply system having an instant hot water function. 
     Referring to  FIG. 1 , a hot water supply system  1 A includes a hot water supply device  100  according to the embodiment, a low-temperature water pipe  110 , a high-temperature water pipe  120 , and a circulation pipe  130 . The hot water supply device  100  has a water inlet port  11 , a hot water outlet port  12 , and a circulation port  13 . 
     Low-temperature water is supplied to the low-temperature water pipe  110  via a check valve  112 . The low-temperature water is typically supplied from a water pipe (not shown). The low-temperature water pipe  110  is connected to the water inlet port  11 . The high-temperature water pipe  120  connects the hot water outlet port  12  and a hot water tap  330 . The circulation pipe  130  connects the high-temperature water pipe  120  and the circulation port  13 . 
     The hot water supply device  100  includes a controller  10 , a water inlet path  20 , a hot water outlet path  25 , a circulation path  28 , a bypass path  29 , a heat source unit  30 , a heat exchanger  40 , a circulation pump  80 , and a flow rate control valve  90 . 
     The water inlet path  20  is formed between the water inlet port  11  and an input side (an upstream side) of the heat exchanger  40  via a check valve  21 . 
     The heat source unit  30  is typically configured by a burner which generates an amount of heat by burning gas, oil, or the like. The heat exchanger  40  raises a temperature of the low-temperature water (a fluid) introduced by the water inlet path  20  using the amount of heat generated by the heat source unit  30 . Therefore, the heat source unit  30  and the heat exchanger  40  can constitute an example of a “heating mechanism.” Alternatively, it is also possible to configure the “heating mechanism” using a heat pump or waste heat generated during power generation. 
     The hot water outlet path  25  is formed between an output side (a downstream side) of the heat exchanger  40  and the hot water outlet port  12 . The bypass path  29  guides some of the low-temperature water to the hot water outlet path  25  by bypassing the heat exchanger  40 . A flow ratio between the bypass path  29  and the heat exchanger  40  can be controlled by an opening command of the flow rate control valve  90  from the controller  10 . Thus, in the hot water outlet path  25 , some of the low-temperature water is mixed downstream of the heat exchanger  40  without being heated, and thus high-temperature water is supplied from the hot water outlet port  12 . 
     In addition, the hot water supply device  100  may be configured without the arrangement of the bypass path  29  and the flow rate control valve  90 , so that the entire amount of the introduced low-temperature water flows through the heat exchanger  40 . However, in the bypass configuration shown in  FIG. 1 , since an output temperature from the heat exchanger  40  (the heating mechanism) can be increased, it is advantageous for curbing drainage generated by exhaust of the heat source unit  30  being cooled on a surface of the heat exchanger  40 . 
     The circulation path  28  is formed between the circulation port  13  and the water inlet path  20  (a connection point  22 ). The circulation pump  80  is connected to the circulation path  28 . Alternatively, the circulation pump  80  may be disposed in the circulation pipe  130  as an external element of the hot water supply device  100 . Regardless of whether the circulation pump  80  is disposed inside or outside the hot water supply device  100 , the operation and stop of the circulation pump  80  are controlled by the controller  10 . 
     A flow rate detector  81  which outputs a flow rate value of the low-temperature water is disposed in the water inlet path  20 , and a flow rate detector  82  is disposed in the circulation path  28 . The flow rate detector  82  may be configured by a sensor which outputs an actual flow rate value similarly to the flow detector  81  or may be configured by a water flow sensor (a switch) which detects the presence or absence of a flow. The values detected by the flow rate detectors  81  and  82  are input to the controller  10 . 
     Further, a temperature detector  71  is disposed in the hot water outlet path  25 , and a temperature detector  72  is disposed in the circulation path  28 . A fluid temperature detected by the temperature detectors  71  and  72  is input to the controller  10 . 
       FIG. 2  is a block diagram showing an example of a hardware configuration of the controller  10 . 
     Referring to  FIG. 2 , the controller  10  is typically configured by a microcomputer. The controller  10  includes a central processing unit (CPU)  15 , a memory  16 , an input/output (I/O) circuit  17 , and an electronic circuit  18 . The CPU  15 , the memory  16 , and the I/O circuit  17  can mutually exchange signals via a bus  19 . The electronic circuit  18  is configured to perform predetermined arithmetic processing by dedicated hardware. The electronic circuit  18  can exchange signals between the CPU  15  and the I/O circuit  17 . 
     The CPU  15  receives output signals (detected values) from sensors including the temperature detectors  71  and  72  and the flow rate detectors  81  and  82  through the I/O circuit  17 . Further, the CPU  15  receives a signal indicating an operation instruction input to a remote controller  95  through the I/O circuit  17 . The operation instruction includes, for example, an on/off operation of an operation switch, a hot water setting temperature, and various time reservation settings (also referred to as “timer reservation settings”) in the hot water supply device  100 . The CPU  15  controls an operation of each component including the heat source unit  30  and the circulation pump  80  so that the hot water supply device  100  is operated according to the operation instruction. 
     Further, the CPU  15  includes a clocking part  15   a  which measures an elapsed time. Furthermore, the CPU  15  can output information, which can be visually or audibly recognized, to a user using a display screen or a speaker (not shown) provided in the remote controller  95 . 
     Electric power of the hot water supply device  100  is supplied from a system power supply  150 . The hot water supply device  100  further includes a power supply circuit  92 . For example, when a plug  93  is connected to an electrical outlet  155  connected to the system power supply  150 , electric power from the system power supply  150  is supplied to the power supply circuit  92 . Hereinafter, a state in which electric power is supplied from the system power supply  150  to the hot water supply device  100  is also referred to as a “power-on state,” a state in which electric power is not supplied from the system power supply  150  to the hot water supply device  100  is also referred to as a “power-off state,” and transition from the power-off state to the power-on state due to a connection of the plug  93  to the electrical outlet is also referred to as “power supply.” 
     In the power-on state, the power supply circuit  92  converts electric power from the system power supply  150  into power supply voltages Vd 1  to Vd 3  supplied to various devices inside the hot water supply device  100 . On the other hand, in the power-off state, since the supply of the power supply voltages Vd 1  to Vd 3  is stopped, the operation of the controller  10  is also stopped. In the power-off state, time measurement by the clocking part  15   a  is also stopped. 
     When the power is supplied, the controller  10  makes the hot water supply device  100  operable by performing a predetermined initial process. Normally, due to the initial process, a time measured by the clocking part  15   a  is cleared to zero. 
     Referring to  FIG. 1  again, the operation of the hot water supply device  100  will be described. 
     At the time of opening a tap, that is, when the hot water tap  330  is opened, the low-temperature water is introduced into the water inlet path  20  by a supply pressure of the low-temperature water. When the flow rate detector  81  detects a flow rate which exceeds a minimum operating flow rate (MOQ) while the operation switch of the hot water supply device  100  is switched on, the controller  10  operates the heat source unit  30 . As a result, the high-temperature water heated by the heat source unit  30  and the heat exchanger  40  is output to the high-temperature water pipe  120  and the hot water tap  330  via the hot water outlet path  25  and the hot water outlet port  12 , and thus a hot water supply operation is performed. During the hot water supply operation, the circulation pump  80  is stopped, and an amount of heating by the heat source unit  30  (the heating mechanism) is controlled so that a fluid temperature (a hot water outlet temperature) detected by the temperature detector  71  is controlled to the hot water setting temperature input to the remote controller  95 . On the other hand, when the flow rate becomes lower than the MOQ due to closing of the tap, or during an OFF period of the operation switch, the hot water supply operation is stopped by the controller  10  stopping the heat source unit  30 . 
     While the hot water supply operation is stopped, since the temperature of the fluid staying in the hot water outlet path  25  and the high-temperature water pipe  120  decreases, there is a concern that, after the next hot water supply operation is started, it will take a long time until the high-temperature water having an appropriate temperature is output from hot water tap  330 . Therefore, an instant hot water function in which the high-temperature water having an appropriate temperature is supplied immediately after the hot water supply operation is started is provided in the hot water supply device  100 . The instant hot water function is realized by operating the circulation pump  80  at the time of closing the tap, that is, when the hot water tap  330  is closed, and thus forming an instant hot water circulation path including the heat source unit  30  and the heat exchanger  40 . 
     For example, during a reservation period of an instant hot water operation mode specified by a user setting a timer reservation setting, when a temperature detected by the temperature detector  71  (the hot water outlet temperature) drops below a start determination temperature Tph 1  while the hot water supply operation is stopped, an instant hot water operation is started. 
     In the instant hot water operation, a fluid path (an internal path) including the circulation port  13 , the circulation path  28 , the water inlet path  20  (on the downstream side from the connection point  22 ), the heat exchanger  40  (the heating mechanism), the hot water outlet path  25 , and the hot water outlet port  12  is formed inside the hot water supply device  100  by operating the circulation pump  80  and the heat source unit  30  (the heating mechanism). Further, since a fluid path (an external path) which bypasses the hot water tap  330  and includes the hot water outlet port  12 , the high-temperature water pipe  120 , the circulation pipe  130 , and the circulation port  13  can be formed outside the hot water supply device  100 , the instant hot water circulation path can be formed in combination with the internal path. As a result, in the hot water supply system  1 A, even when the tap is closed, the hot water supply operation of the high-temperature water having an appropriate temperature can be started immediately after the tap is opened by allowing the high-temperature water having the appropriate temperature to flow through the instant hot water circulation path. 
     When the hot water outlet temperature rises above a termination determination temperature Tph 2  (Tph 2 &gt;Tph 1 ) with the instant hot water operation, the instant hot water operation is ended by stopping the heat source unit  30  and the circulation pump  80 . That is, during the reservation period of the instant hot water operation mode, the instant hot water operation is automatically started and ended. A user can directly input and set the reservation period by operating the remote controller  95 , for example. Alternatively, the reservation period of the instant hot water operation mode may be automatically set by learning a past use history of the user. 
     The circulation pump  80  is stopped except during the performing of the instant hot water operation. Thus, there is a possibility that the circulation pump  80  may be stopped continuously for a long period of time because an instant hot water reservation period is not set in the summer or the like or when the water temperature is high. According to water quality, when such long-term stoppage occurs, there is a concern that an inorganic salt compound (so-called scale) such as calcium in water may adhere around a bearing of the circulation pump  80 . When the adhesion of scale becomes remarkable, there is a concern that the circulation pump  80  may become unusable due to fixation of a rotating shaft. 
     Therefore, in the hot water supply device according to the embodiment, an operation for protecting the circulation pump  80  from the adhesion of scale (hereinafter, also simply referred to as a “protection operation”) is performed. The protection operation does not require use of a cleaning agent and does not require a long time, unlike the cleaning operation in Patent Literature 1. Therefore, the protection operation according to the embodiment can be performed while allowing intervention of the hot water supply operation. 
       FIG. 3  is a state transition diagram of the protection operation of the circulation pump by the hot water supply device according to Embodiment 1. 
     Referring to  FIG. 3 , in a state in which the protection operation of circulation pump  80  is not performed (hereinafter referred to as a “protection operation OFF state”), the circulation pump  80  is stopped. In the protection operation OFF state, when both a condition XA regarding a stop history of the circulation pump  80  and a condition XB regarding the stop of the operation of the hot water supply device  100  are satisfied, the protection operation of operating the circulation pump  80  is performed. Accordingly, a transition from the protection operation OFF state to a protection operation ON state occurs. 
       FIG. 4  is a chart showing a list of content of each of the conditions shown in  FIG. 3 . 
     Referring to  FIG. 4 , the condition XA is satisfied when the circulation pump  80  has been stopped for at least T 1  (for example, T 1 =24 (hours)) since the last stop. Whether or not the condition XA is satisfied can be determined by measuring an elapsed time from the stop of the circulation pump  80  with the clocking part  15   a . The condition XA corresponds to one example of a “first condition,” and T 1  corresponds to one example of a “first time.” 
     The condition XB is satisfied when the hot water supply operation is stopped (the hot water supply operation is turned off) and is not satisfied when the hot water supply operation is being performed (the hot water supply operation is turned on) (that is, a condition /XB is satisfied). An ON period of the hot water supply operation may be defined to include not only a period during which the heating by the heat source unit  30  is performed, but also a period after the heating is stopped (for example, a purge period of an exhaust gas). 
     Alternatively, the condition XB may be satisfied when the hot water supply operation is stopped and the instant hot water operation is out of the reservation period. In this case, the condition XB is not satisfied when the hot water supply operation is being performed or during the reservation period for the instant hot water operation (the condition /XB is satisfied). The condition XB corresponds to an example of a “second condition.” 
     Referring again to  FIG. 3 , in the protection operation ON state, the circulation pump  80  is operated, and thus the instant hot water circulation path is formed. Accordingly, it is possible to prevent scale from adhering around the bearing of the circulation pump  80 . 
     In the protection operation ON state, a protection operation completion flag PFlg is operated according to a flowchart shown in  FIG. 5 . 
     Referring to  FIG. 5 , the controller  10  determines whether or not the protection operation of the circulation pump  80  is started in Step (hereinafter, simply referred to as “S”)  110 . YES is determined in S 110  when a transition from another state to the protection operation ON state occurs in  FIG. 3 , and otherwise NO is determined. 
     The controller  10  clears the protection operation completion flag PFlg is cleared to 0 in S 120  at the start of the protection operation in which the circulation pump  80  is operated (YES in S 110 ). At this point, it is possible to clear the value measured by the clocking part  15   a.    
     In the protection operation ON state ( FIG. 3 ), the protection operation completion flag PFlg=0 is set to “0” or “1” according to whether or not conditions of S 130  to S 150  are satisfied. In S 130 , the controller  10  determines whether T 2  (for example, T 2 =1 to 3 (minutes)) has elapsed from the start of the protection operation (a condition YA) according to the value measured by the clocking part  15   a . When the condition YA is satisfied, the circulation pump  80  has been operated continuously for T 2 . T 2  corresponds to an example of a “second time.” The condition YA corresponds to a basic termination condition of the protection operation. 
     Further, in S 140 , the controller  10  detects whether the circulation pump  80  is being operated in a state in which no fluid is present (a so-called idling state) by determining whether or not a condition YB is satisfied. For example, the condition YB is satisfied when a state in which a flow rate (the flow rate detector  82 ) of the instant hot water circulation path is equal to or less than a determination flow rate Qx is continuously detected for a determination time Tx. 
     In S 150 , the controller  10  determines whether or not T 3  (T 3 &lt;T 2 ) has elapsed from the start of the protection operation (a condition YC) according to the value measured by the clocking part  15   a . Furthermore, the conditions YA to YC in S 130  to S 150  are described in  FIG. 4  together with the above conditions XA and XB (/XB). T 3  corresponds to an example of a “third time.” 
     The controller  10  sets the protection operation completion flag PFlg=1 in S 160  when YES is determined in at least one of S 130  to S 150  in the protection operation ON state, that is, when at least one of the conditions YA to YC is satisfied. On the other hand, when NO is determined in all of S 130  to S 150 , that is, when none of the conditions YA to YC are satisfied, the protection operation completion flag PFlg=0 is maintained in S 170 . 
     Therefore, although the circulation pump  80  is not continuously operated over T 2  in S 130  (that is, the condition YA is not satisfied), the condition YC is satisfied when the operation is continuously performed for T 3  shorter than T 2 . When the protection operation completion flag PFlg=1, the processing of the flowchart in  FIG. 5  is restarted, and the protection operation completion flag PFlg=1 is maintained until the next protection operation is started (until YES is determined in S 110 ). 
     Referring to  FIG. 3  again, when condition YA, YB or /XB is satisfied in the protection operation ON state, the circulation pump  80  is stopped. Further, the transition to the protection operation OFF state or an interruption state occurs according to the protection operation completion flag PFlg at this point. In particular, when the hot water supply operation is started during the protection operation (when the condition XB is not satisfied), the circulation pump  80  is stopped, and an intervention process which gives priority to the hot water supply operation can be performed. In addition, as described with reference to  FIG. 4 , when the condition XB includes that it is out of the reservation period of the instant hot water operation, the intervention process which gives priority to the instant hot water operation can be further performed. 
     When the condition YA is satisfied in the protection operation ON state, YES is determined in S 130  in  FIG. 5 , and PFlg=1 is set (S 160 ), and thus the transition from the protection operation ON state to the protection operation OFF state occurs. In this case, the continuous operation time T 2  of the circulation pump  80  is ensured, and the protection operation is ended normally. 
     When the condition /XB is satisfied in the protection operation ON state (that is, when the condition XB is not satisfied), a value of the protection operation completion flag PFlg differs according to whether or not the condition YC in S 150  is satisfied. That is, when the continuous operation time of the circulation pump  80  is T 3  or more (T 3 &lt;T 2 ), PFlg=1, and when it does not reach T 3 , PFlg=0. 
     When the protection operation completion flag PFlg=0, that is, when the condition XB is not satisfied before the continuous operation time of the circulation pump  80  reaches T 3 , a transition from the protection operation ON state to the interruption state occurs. In the interruption state, the resumption of the protection operation is awaited, and when the condition XB is satisfied again according to the stop of the hot water supply operation (or the termination of the instant hot water reservation period), the transition to the protection operation ON state occurs. Accordingly, the circulation pump  80  is started, the protection operation is automatically started, and YES is determined in S 110  in  FIG. 5 . 
     On the other hand, when the condition XB is not satisfied after the continuous operation time of the circulation pump  80  is ensured for T 3  or more, the protection operation completion flag PFlg=1, and thus the transition from the protection operation ON state to the protection operation OFF state occurs. In this case, the next protection operation is not performed until the elapsed time from the stop of the circulation pump  80  reaches T 1  (the condition XA). 
     Also when the condition YB is satisfied in the protection operation ON state, that is, when the idling of the circulation pump  80  is detected due to the protection operation, YES is determined in S 140  in  FIG. 5 , and PFlg=1 is set (S 160 ), and thus the transition from the protection operation ON state to the protection operation OFF state occurs. Also in this case, the next protection operation is not performed until the time elapsed from the stop of the circulation pump  80  reaches T 1  (the condition XA). Thus, it is possible to prevent the protection operation from being repeatedly restarted in a short period of time even when the idling state is detected. 
       FIG. 6  is a waveform diagram showing an operation example of the protection operation of the circulation pump by the hot water supply device according to Embodiment 1. 
     Referring to  FIG. 6 , at time ta, when the elapsed time from the previous stop of the circulation pump  80  reaches T 1  (that is, the condition XA is satisfied), the hot water supply operation is being stopped (that is, the condition XB is satisfied), and thus the transition from the protection operation OFF state to the protection operation ON state occurs. Accordingly, the circulation pump  80  operates to start the protection operation. With the start of the protection operation, the protection operation completion flag PFlg is cleared to 0 (S 120 ). 
     When the hot water supply operation is started at time tb before T 2  and T 3  elapse from the time ta, the condition XB is not satisfied (the condition /XB is satisfied), and thus the circulation pump  80  is stopped. At the time tb, since the protection operation completion flag PFlg=0, the transition from the protection operation ON state to the interruption state in  FIG. 3  occurs. 
     At time tc, when the hot water supply operation is stopped, the transition from the interruption state to the protection operation ON state in  FIG. 3  occurs, the circulation pump  80  is operated again, and the protection operation is restarted. Thereafter, at time te when T 2  has elapsed from the time tc, the condition YA is satisfied, the circulation pump  80  is stopped, and the protection operation is ended. At this time, the transition from the protection operation ON state to the protection operation OFF state occurs. 
     On the other hand, the protection operation completion flag PFlg is changed from 0 to 1 by the determination in S 150  in  FIG. 5  being YES at time td when T 3  has elapsed from the time tc, that is, at a timing earlier than time te. 
     Here, as shown by a dotted line in  FIG. 6 , it is assumed that the hot water supply operation is performed at time tx between times td and te, and the hot water supply operation is stopped at time ty after time tx. In this case, at time tx, the circulation pump  80  is stopped for the intervention process of the hot water supply operation. However, since the protection operation completion flag PFlg has already been changed to 1, the transition from the protection operation ON state to the protection operation OFF state in  FIG. 3  occurs at this point. Therefore, even when the hot water supply operation is stopped at the time ty, the protection operation by the operation of the circulation pump  80  is not restarted as at the time tc. 
     As described above, according to the hot water supply device according to Embodiment 1, whenever a continuous stop time of the circulation pump  80  reaches a predetermined value (T 1 ), priority is given to the hot water supply operation (and the instant hot water operation), and then the protection operation can be performed at an appropriate timing. As a result, in the hot water supply device having the instant hot water function, the protection operation of the circulation pump  80  for preventing the adhesion of the scale can be efficiently and appropriately performed. 
     Also, during the protection operation, the hot water supply operation (and the instant hot water operation) can be prioritized by the intervention process. After the hot water supply operation (and the instant hot water operation) is ended, the protection operation can be automatically performed again. On the other hand, when the continuous operation time of the circulation pump  80  is secured for T 3  (T 3 &lt;T 2 ) at the time of occurrence of the intervention, or when the idling of the circulation pump  80  is detected, the protection operation is ended as it is, and thus it is possible to prevent the protection operation from being excessively repeated. 
     Embodiment 2 
     In Embodiment 1, a start trigger of the protection operation is generated on the basis of the elapsed time since the circulation pump  80  was stopped. However, the measurement of the elapsed time is based on a continuous power-on state in which the connection of the plug  93  is maintained, as described with reference to  FIG. 2 . 
     Meanwhile, a usage mode in which the plug  93  is disconnected from the system power supply  150  whenever the use of the hot water supply device  100  is ended, and the electric power is turned on whenever the use of the hot water supply device  100  is started, is also assumed according to the user. On the other hand, under such a usage mode, in the hot water supply device according to Embodiment 1, it is difficult to measure the elapsed time, and thus it is difficult to appropriately perform the protection operation of the circulation pump  80 . 
       FIG. 7  is a state transition diagram of the protection operation of the circulation pump by the hot water supply device according to Embodiment 2, and  FIG. 8  is a chart showing a list of contents of each of conditions shown in  FIG. 7 . 
     Referring to  FIGS. 7 and 8 , in the hot water supply device according to Embodiment 2, in addition to the conditions XA and XB (/XB) and the conditions YA to YC similar to those in Embodiment 1, a condition XC relating to power supply is further set. 
     The condition XC is satisfied for a certain period (for example, about several tens of seconds) when T 4  (for example, about 5 to 10 seconds) has elapsed since the power supply of the hot water supply device  100  was turned on. In a period (the power-on state) after the elapse of the certain period, the condition XC is not satisfied. Whether or not the condition XC is satisfied can also be determined on the basis of the value measured by the clocking part  15   a  of which the operation is started in response to the power supply. T 4  corresponds to an example of a “fourth time”. 
     In the hot water supply device according to Embodiment 2, the transition from the protection operation OFF state to the protection operation ON state occurs not only when the conditions XA and XB equivalent to those in Embodiment 1 are satisfied but also when the conditions XC and XB relating to a certain period after the power supply is turned on are satisfied. On the other hand, a condition relating to the transition from the protection operation ON state to another state is the same as in Embodiment 1. 
     As a result, according to the hot water supply device according to Embodiment 2, since the power supply is turned off whenever the use of the hot water supply device  100  is ended, even under a usage mode in which it is difficult to accurately measure the elapsed time since the circulation pump  80  is stopped with the clocking part  15   a , it is possible to appropriately secure an opportunity for the protection operation of the circulation pump  80 . 
     [Modified Example of Hot Water Supply Device] 
       FIG. 9  is a block diagram showing a configuration of a hot water supply system including a hot water supply device according to a modified example of the present embodiment. 
     Referring to  FIG. 9 , a hot water supply system  1 B includes a hot water supply device  100 X according to a modified example of the present embodiment, a low-temperature water pipe  110 , and a high-temperature water pipe  120 . The hot water supply device  100 X has a water inlet port  11  and a hot water outlet port  12  without having a circulation port  13 . Therefore, unlike the hot water supply device  100  of  FIG. 1 , the circulation path  28  is not provided inside the hot water supply device  100 X. 
     Other configurations of the hot water supply device  100 X are the same as those of the hot water supply device  100 , and thus detailed description thereof will not be repeated. Also in the hot water supply device  100 X, it is possible to omit the arrangement of the bypass path  29  and the flow rate control valve  90  and to configure so that the entire amount of the introduced low-temperature water flows through the heat exchanger  40 . 
     In the hot water supply system  1 B, low-temperature water is supplied to the low-temperature water pipe  110  via a check valve  112 . The low-temperature water pipe  110  is connected to the water inlet port  11 . The high-temperature water pipe  120  connects between the hot water outlet port  12  and a hot water tap  330 . The circulation pipe  130  connects between the high-temperature water pipe  120  and the low-temperature water pipe  110 . 
     The circulation pump  80  can be connected to the circulation pipe  130 . During the hot water supply operation in which the circulation pump  80  is stopped, when the hot water tap  330  is opened, at least some of the low-temperature water introduced from the low-temperature water pipe  110  to the water inlet port  11  is heated by the heating mechanism (a heat source unit  30  and a heat exchanger  40 ). The high-temperature water obtained by the heating is output from the hot water tap  330  through the hot water outlet port  12  and the high-temperature water pipe  120 . Accordingly, the hot water supply operation can be performed also in the hot water supply device  100 X, similarly to the hot water supply device  100 . 
     Meanwhile, when the circulation pump  80  is operated at the time of closing the tap, a fluid path (an internal path) including the water inlet port  11 , the water inlet path  20 , the heat exchanger  40  (the heating mechanism), the hot water outlet path  25 , and the hot water outlet port  12  can be formed inside the hot water supply device  100 . Further, a fluid path (an external path) which bypasses the hot water tap  330  via the hot water outlet port  12 , the high-temperature water pipe  120 , the circulation pipe  130  and the low-temperature water pipe  110  and reaches the water inlet port  11  can be formed outside the hot water supply device  100 . As a result, the instant hot water circulation path can also be formed in the hot water supply system  1 B. 
     Also in hot water supply system  1 B, the similar protection operation can be performed by controlling the circulation pump  80  according to Embodiment 1 or 2. In this way, also in the hot water supply device  100 X without the circulation port  13 , the protection operation of the circulation pump  80  for preventing the adhesion of the scale can be efficiently and appropriately executed. 
     Further, in the hot water supply systems  1 A and  1 B, the circulation pump  80  is not limited to the examples shown in  FIGS. 1 and 9  as long as it can form the same instant hot water circulation path as described above, and the circulation pump  80  may be located anywhere outside or inside the hot water supply devices  100  and  100 X. That is, also in a configuration in which the circulation pump  80  is not built in the hot water supply devices  100  and  100 X, the provision of the controller  10  for controlling the stop and the operation of the circulation pump  80  allows a test mode according to the embodiment to be realized. 
     It will be apparent to those skilled in the art that various modifications and variations can be made to the disclosed embodiments without departing from the scope or spirit of the disclosure. In view of the foregoing, it is intended that the disclosure covers modifications and variations provided that they fall within the scope of the following claims and their equivalents.