Patent Publication Number: US-2012037095-A1

Title: Hot water mixing valve with failure detection

Description:
BACKGROUND 
     This disclosure relates to mixing valves for reducing or limiting the temperature of outgoing hot water, and in particular, to a hot water mixing valve with failure detection. The exemplary mixing valve with failure detection finds particular application in conjunction with water heaters, and will be described with particular reference thereto. However, it is to be appreciated that the exemplary mixing valve with failure detection is also amenable to other like applications. 
     Mixing valves are, in general, well known and a typical mixing valve comprises a through channel which is connected in series with a hot water supply line. A cold water inlet communicates with the through channel at an upstream side of a thermostat element. The thermostat element is located in the channel and functions to control the temperature of water passing from the mixing valve. A regulator valve element is located in a fluid passage between the cold water inlet and the through channel. The regulator valve element is controlled by the thermostat element to regulate the quantity of cold water which is admitted into the through channel to mix with the hot water. The thermostat element senses the temperature of the hot-and-cold water mix and controls the regulator valve element to provide a mix ratio that results in a required (pre-determined) outflow temperature. The thermostat element is typically adjustable to provide for the required outflow temperature. 
     It is known in the art to provide a mixing valve connected between a cold water inlet line and a hot water outlet line remote from or immediately adjacent a water heater. Water heaters are normally set to temperatures above 131° F. (55° C.) to prevent development of bacteria, such as Legionella, in the water supply. The mixing valve is operable to detect the temperature of the water in the hot water line and to introduce cold water into the hot water line when the hot water temperature is too high, thereby reducing the temperature of the hot water delivered. 
     In some cases, the water heater thermostat is faulty, or set too high. In others, the mixing valve can be malfunctioning. Prior art mixing valves are typically incapable of failure detection. For example, in the known mixing valves which use a wax-filled thermostat element, the regulating valve element will not be actuated and, in a worst case situation, no cold water will be admitted into the hot water stream if the thermostat element fails to function as a result of wax bleeding away from such element. The temperature of the outflowing water will then be approximately equal to that of the inflowing hot water. For at least this reason, and because of the lack of failure detection, regular inspection of the prior art mixing valve is recommended to assure a properly functioning mixing valve. 
     BRIEF DESCRIPTION 
     According to one aspect, a mixing valve comprises a housing including first and second inlet passages and a third, outlet passage. The first passage is connectable in a high temperature fluid supply line. The second passage is connectable with a low temperature fluid supply. The third passage selectively communicates with the first and second passages. A valve assembly is mounted within the housing and includes a thermostat element and a valve body actuatable by the thermostat element. The thermostat element is in thermal contact with the high temperature fluid passing through the first passage. The valve body is operable under the influence of the thermostat element to regulate flow of low temperature fluid and provide a mix ratio of high temperature fluid and low temperature fluid that results in a mixed fluid having a selected temperature flowing out of the third passage. The mixing valve is adapted to provide feedback to a consumer of a failure condition. 
     According to another aspect, a mixing valve comprises a housing including first and second inlet passages, a third, outlet passage and a mixing chamber. The first passage is connectable to a source of relatively hot water. The second passage is connectable with a source of relatively cold water. The third passage selectively communicates with the first and second passages. The mixing chamber selectively communicates with the first, second and third passages. A valve assembly mixes the hot water with the cold water for providing mixed water at a selected, adjustable temperature for the third passage. The valve assembly is controllable to maintain the mixed water at the selected temperature. The valve assembly provides user feedback of a failure condition by providing one of a limited flow of relatively hot water and a flow of low temperature water through the third passage. The valve assembly prevents a high flow rate of relatively hot water through the third passage during the failure condition. 
     According to yet another aspect, a water heater comprises a body defining a chamber for holding water to be heated, a heater for heating the water in the chamber to a threshold temperature, and an inlet opening and an outlet opening in communication with the chamber for flowing water therethrough. An inlet line extends through the inlet opening and into the chamber for admitting relatively cold water into the chamber. An outlet line extends through the outlet opening for permitting flow of relatively hot water from the chamber. A mixing valve includes first and second inlet passages and an outlet passage. The first passage is in fluid communication with the inlet line. The second passage is in fluid communication with the outlet line. The outlet passage is in selective fluid communication with the first and second passages. A valve assembly mixes the relatively hot water with the relatively cold water to provide a flow of mixed water at a selected temperature through the third passage. The valve assembly includes a thermostat element and a valve body actuatable by the thermostat element. The valve body includes a first valve member for regulating flow of the relatively hot water and a second valve member for regulating flow of the relatively cold water. The valve body provides user feedback of a failure condition by delivering one of a limited flow of hot water and a flow of low temperature water through the mixing valve. The valve body prevents a high flow rate of the relatively hot water through the mixing valve during the failure condition. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic of a known water heater. 
         FIG. 2  is a schematic of a known mixing valve for the water heater of  FIG. 1 . 
         FIG. 3  is a schematic of an exemplary new mixing valve for use in the water heater of  FIG. 1  according to one aspect of the present disclosure in a no flow condition. 
         FIG. 4  is a schematic of the exemplary mixing valve of  FIG. 3  in a hot water initial state condition. 
         FIG. 5  is a schematic of the exemplary mixing valve of  FIG. 3  in a failure condition. 
         FIG. 6  is a schematic of the exemplary mixing valve of  FIG. 3  in a hot water demand full flow condition. 
         FIG. 7  is a schematic of an exemplary mixing valve for the water heater of  FIG. 1  according to another aspect of the present disclosure, where the exemplary mixing valve is in a hot water initial state condition. 
         FIG. 8  is a schematic of the exemplary mixing valve of  FIG. 7  in a hot water demand full flow condition. 
         FIG. 9  is a schematic of another exemplary mixing valve for the water heater of  FIG. 1  according to yet another aspect of the present disclosure, where the exemplary mixing valve is in a hot water initial state condition. 
         FIG. 10  is a schematic of the exemplary mixing valve of  FIG. 9  in a hot water demand full flow condition. 
     
    
    
     DETAILED DESCRIPTION 
     Referring now to the drawings, wherein like numerals refer to like parts throughout the several views,  FIG. 1  generally depicts a known water heater  100 . The water heater  100  includes a tank or body  110  having an interior chamber or elongated hollow (not shown) for receiving relatively cold water. An inlet line 112  extends through an upper portion, particularly a top wall  116 , of the tank and into the chamber for admitting relatively cold water into a lower portion of the chamber. An outlet line  120  extends through the upper portion of the tank for permitting flow of relatively hot water from the chamber. A heater (not shown) is operatively associated with the chamber for heating the water within the chamber to a user selected setpoint temperature. The heater preferably comprises one of an electrically driven heating element, a heat pump having a heat exchange system, and/or a gas burner positioned proximate a lower portion of the tank  110 . A control panel or user interface (not shown) is provided on the water heater  100  and typically includes a user interface for making various operational selections, such as setting the setpoint temperature of the water heater. 
     A known mixing valve  150  for the water heater  100  is schematically illustrated in  FIG. 2 . Typically, the mixing valve  150  is connected between the inlet line  112  and the outlet line  120  remote from or immediately adjacent the water heater  100 . The mixing valve  150  is operable to detect the temperature of the relatively hot water flowing through the outlet line  120  and introduce relatively cold water flowing through the inlet line  112  into the outlet line when the water temperature is too high. This reduces the temperature of the relatively hot water being delivered from the water heater  100 . 
     With reference to  FIG. 2 , the known mixing valve  150  comprises a housing  152  including first and second inlet passages  154 ,  156  and an outlet passage  158 . The first inlet passage  154  is connectable to a first section  160  of the outlet line  120  to receive hot water. The second inlet passage  154  is connectable with the inlet line  112  to receive cold water. The outlet passage  158  is connectable to a second section  162  of the outlet line  120  and is in selective fluid communication with the first and second inlet passages  154 ,  156  to provide water at a desired temperature. The housing  152  further includes a water mixing chamber  166 . The mixing chamber has a relatively hot water inlet  168  in fluid communication with the first inlet passage  154 , a relatively cold water inlet  170  in fluid communication with the second inlet passage  156  and a mixed water outlet  172  in fluid communication with the outlet passage  158 . 
     The mixing valve  150  further includes what is generally referred to as a wax motor or a valve assembly  180  moveably mounted within the mixing chamber  166 . The valve assembly  180  includes a thermostat element  182 , a regulator valve element  184  that is operatively connected to and actuatable by the thermostat element and a biasing member, such as a spring  186 . The regulator valve element  184  includes a body  190  having an inlet opening  192  and an outlet opening  194 . The inlet opening  192  is positioned adjacent a wall  196  of the housing  152  and is in selective fluid communication with the relatively cold water inlet  170 . In a closed position, the body  190  abuts the wall  196  to prevent the flow of relatively cold water through the body  190  and into the mixing chamber. In an open position, the body  190  is spaced from the wall  196  allowing the flow of relatively cold water into the mixing chamber  166 . The outlet opening  194  is in fluid communication with the mixed water outlet  172 . 
     The thermostat element  182  extends through the body  190  and has a first end section proximate the housing wall  196  and a second end section operatively coupled to the spring  186 . Linear movement of the regulator valve element  184  in response to thermal expansion of the thermostat element  182  in a first direction within the mixing chamber  166  moves the regulator valve element away from the housing wall  196 . As the regulator valve element moves in the first direction, the body  190  restricts the flow of relatively hot water through the inlet  168 . This allows relatively cold water to flow into the inlet opening  192  through the body  190  and to the outlet opening  194  for mixing with the relatively hot water. Linear movement of the regulator valve element  184  in response to thermal contraction of the thermostat element  182  in a second direction within the mixing chamber  166  moves the regulator valve element towards the housing wall  196 . This limits or prevents the flow of relatively cold water through the body  190  for mixing with the relatively hot water flowing through the inlet  168 . 
     The thermostat element  182  functions to control the temperature of the relatively hot water passing from the mixing valve  150 . Typically, the thermostat element  182  is of the type which operates by thermal expansion and can be charged with wax or other similar material which has a high coefficient of thermal expansion. The thermostat element  182  is contactable thermally by the relatively hot water passing through the first inlet passage  154  and into the mixing chamber  166  via the inlet  168 . The regulator valve element  184  is actuated by the thermostat element  182  to regulate the quantity of relatively cold water which is admitted into the mixing chamber  166  via inlet  170  to mix with the relatively hot water. The thermostat element  182  is responsive to the temperature of the hot-and-cold water mix and contracts/expands which actuates the regulator valve element  184  to provide a mix ratio that results in a required or predetermined outflow water temperature (i.e., the user selected setpoint temperature). The thermostat setpoint is generally controlled by the spring  186  with user adjustment on spring compression. The spring  186  acts to urge the valve body  190  in the upward position of  FIG. 2  which serves to restrict or shut-off the cold water inlet. 
     More particularly, in use, when the thermostat element  182  is exposed to a temperature increase, the wax or other material within the thermostat element is caused to expand. This expansion will act to move the valve body against the spring. The user selected setpoint for output temperature is based on the compression of the spring. The valve body moves with the expansion of the wax and further compresses the spring. As the valve body moves it opens a cold water inlet thus reducing the temperature of the water and thus regulating the outlet water temperature lower. Conversely a temperature decrease will cause the wax to contract reducing the force on the spring and thus the valve body will move to allow less cold water in the system thus regulating the outlet temperature higher. The user selected setpoint temperature, the wax or other material within the thermostat element is caused to expand. This expansion acts against the spring  186  allowing the regulator valve element  184  to move in the first direction within the mixing chamber  166 . This movement of the regulator valve element  184  allows the cold water inlet  170  to open more fully and at the same time restricts the hot water inlet  168 . Conversely, when the thermostat element is exposed to temperatures less than the user selected setpoint temperature, the wax or other material within the thermostat element  182  will contract. This contraction causes the spring  186  to move the regulator valve element  184  in the second direction within the mixing chamber  166 . This movement of the regulator valve element  184  restricts the cold water inlet  170  and at the same time allows the hot water inlet  168  to open more fully. Thus, the known mixing valve  150  automatically and continually maintains the mixed outlet water temperature at the user selected setpoint temperature within the tolerances of the mixing valve. 
     However, with this known construction, the mixing valve  150  does not include failure detection and fails to provide a low temperature outflow in the event that the valve assembly  180  should malfunction. For example, hard water particulates can build up on an inner surface of the walls of the housing  152 , specifically within the mixing chamber  166 , which in turn could restrict or prevent movement of the regulator valve element  184  upon expansion of the thermostat element  182 . If the regulating valve element  184  is not actuated, no cold water will be admitted into the mixing chamber  166 . The temperature of the outflowing water will then be greater than the user selected setpoint temperature for the mixed water. For at least this reason, regular inspection of the prior art mixing valve  150  is recommended to assure a properly functioning system. Corrosive water conditions, unauthorized adjustments or repairs can be detected during inspection and service of the mixing valve  150 . The frequency of inspection and cleaning generally depends upon local water conditions. 
     With reference to  FIG. 3 , a mixing valve  200  according to one aspect of the present disclosure is schematically illustrated. Similar to the known mixing valve  150 , the exemplary mixing valve  200  is connected between the relatively cold water inlet line  112  and the relatively hot water outlet line  120  associated with the water heater  100 . The mixing valve  200  is operable to detect the temperature of the water flowing through the outlet line  120  and to introduce cold water into the outlet line when the water temperature is too high, thereby reducing the temperature of the relatively hot water delivered. Unlike the known mixing valve  150 , the exemplary mixing valve  200  is adapted to provide feedback to a consumer of a failure condition. 
     The exemplary mixing valve  200  comprises a housing  202  including first and second inlet passages  204 ,  206  and an outlet passage  208 . The first inlet passage  204  is connectable to the first section  160  of the outlet line  120 . The second inlet passage  206  is connectable with the inlet line  112 . The outlet passage  208  is connectable to the second section  162  of the outlet line  120  and is in selective fluid communication with the first and second inlet passages  204 ,  206 . In the depicted exemplary embodiment, the first inlet passage  204  is oriented generally perpendicular to the second inlet passage  206 , although alternative configurations are contemplated. The housing  202  further defines a mixing chamber  216 . The mixing chamber has a relatively hot water inlet  218  in fluid communication with the first inlet passage  204 , a relatively cold water inlet  220  in fluid communication with the second inlet passage  206  and a mixed water outlet  222  in fluid communication with the outlet passage  208 . 
     The mixing valve  200  includes a wax motor or valve assembly  230  which is at least partially received within the mixing chamber  216 . The valve assembly  230  is controllable to maintain the mixed water at the user selected, adjustable setpoint temperature for the water heater  100 . As will be discussed in greater detail below, the valve assembly  230  provides user feedback of a failure condition by providing one of a limited flow of relatively hot water and a flow of low temperature water through the third passage  208 . The valve assembly prevents a high flow rate of relatively hot water through the third passage during the failure condition. 
     The valve assembly  230  includes a thermostat element  232 , a valve body  234  actuatable by the thermostat element and a biasing member, such as a spring  236 . Similar to thermostat element  182 , thermostat element  232  operates by thermal expansion and can be charged with wax or other similar material which has a high coefficient of thermal expansion. The valve body  234  is adapted to only allow a fixed flow of hot temperature fluid from the first inlet passage  204  upon initial demand. The thermostat element  232  has an adjustable setpoint temperature which determines the temperature of the mixed fluid flowing out of the third passage. Typically, adjustment of the setpoint temperature is controlled by compressing the spring  236  that biases the valve body  234  upwardly within the mixing chamber  216 . The setpoint temperature of the thermostat element typically is lower than the user selected setpoint temperature for the water heater  100 . As is well known, a mechanical adjustment permits selection of the desired outlet water temperature within a range of the mixing valve  200 . The valve body  234  is configured to deliver the limited flow of relatively hot water to the thermostat element  232  to heat the thermostat element to the setpoint temperature. The valve body  234  is displaceable within the mixing chamber  216  due to its operative engagement with and under the influence of the thermostat element to simultaneously regulate the flow of relatively hot water from the first inlet passage  204  and flow of relatively cold water from the second inlet passage  206  into the mixing chamber upon full demand. The valve body  234  is configured to prevent a high flow rate of hot temperature fluid through the third passage  208  upon failure of the valve assembly  230 . 
     More particularly, and with reference to  FIGS. 3 and 4 , the valve body  234  includes a first valve member  240  and a second valve member  242  which is operatively associated with or connected to the first valve member  240 . According to one aspect, the first and second valve members  240 ,  242  form a unitary valve body. According to another aspect, the first valve member  240  can be attached to the second valve member  242  in a conventional manner. As a result of this operative connection, the second valve member  242  moves simultaneously with the first valve member  240 . This provides a single moving component within the mixing valve  200  for regulating temperature of the mixed water and provides user feedback of the failure condition such as a malfunctioning valve assembly  230 . 
     As shown in  FIGS. 3 and 4 , the first valve member  240  is located outside the mixing chamber  216  and is associated with the first inlet passage  204  for regulating flow of the relatively hot water flowing through the outlet line  120 . The first valve member  240  extends outwardly from the second valve member  242  and includes a first portion  244  connected to the second valve member  242  and a second portion  246  selectively engageable with a valve seat  250  formed in the first inlet passage  204 . The first valve portion  244  and the seat  250  are generally configured as high flow rate valves. The first valve member  240  is configured to allow only a limited flow of the high temperature water upon initial user demand from the first inlet passage  204 . To this end, the first valve member includes an orifice  260  located in the second portion  246  and dimensioned to allow the limited flow of the relatively hot water upon initial demand from the first inlet passage  204  through the outlet passage  208 . The fixed flow orifice  260  is adapted to limit the flow to a set flow rate under varying pressure drops. In the exemplary embodiment, the orifice  260  is preferably and centrally positioned on the second portion  246  and provides for less than about 0.5 gpm, more preferably about 0.25 gpm, of relatively hot water through the first valve member upon initial demand. Ideally, the initial flow rate will be tuned to a minimum value that will provide adequate response time for the thermostatic element to actuate. Alternatively, the first valve portion  244  can be configured to open slightly due to the differential pressure on the supply side line  160  and the outlet  162 . Further, the orifice  260  can be configured to be self cleaning as is commonly known. 
     The second valve member  242  is located at least partially within the mixing chamber and is operatively associated with the thermostat element  232 . The second valve member  242  is associated with the second inlet passage  206  for regulating flow of the relatively cold water flowing through the inlet line  112 . The second valve member  242  is similar to the regulator valve element  184  described in connection with  FIG. 2  and includes an inlet opening  270  and an outlet opening  272 . The inlet opening  270  is positioned adjacent a wall  276  of the housing  202  and is in selective fluid communication with the relatively cold water inlet  220 . In a closed position ( FIG. 4 ), the second valve member  242  abuts the wall  276  to limit or prevent the flow of relatively cold water through the second valve member and into the mixing chamber  216 . In an open position ( FIG. 6 ), the second valve member  242  is spaced from the wall  276  thereby allowing the flow of relatively cold water into the mixing chamber  216 . The outlet opening  272  is in fluid communication with the mixed water outlet  222 . A seal  280  can be provided to prevent leaking of the relatively cold water into the mixing chamber. 
     The thermostat element  232  extends through the second valve member  242  and has a first end section proximate or abutting the housing wall  276  and a second end section operatively coupled to the spring  236 . The thermostat element  232  is in thermal contact with the high temperature fluid passing through the first inlet passage  204 . The valve body  234  is operable under the influence of the thermostat element to regulate flow of the low temperature fluid and provide a mix ratio of high temperature fluid and low temperature fluid that results in a mixed fluid having a selected or predetermined temperature flowing out of the third passage  208 . 
     As shown in  FIG. 4 , upon initial demand, the first valve member  240  and the second valve member  242  are in a closed position. The orifice  260  of the first valve member  240  provides for a low flow of relatively hot water through the first valve member. This low flow of relatively hot water flows through the first passage  204 , the inlet  218  and into the mixing chamber  216 . The limited flow of the high temperature water is delivered to the thermostat element  232  for heating the thermostat element to its selected setpoint temperature, which is lower than the temperature of the relatively hot water. As shown in  FIG. 6 , in a normal operating condition (i.e., full demand), when the thermostat element  232  is exposed to the high temperature water, the wax or other material within the thermostat element is caused to expand. This expansion acts against and overcomes the bias of the spring  236  that urges the second valve member toward a closed position and allows the second valve member  242  to move in a first direction within the mixing chamber  216  away from the housing wall  276 . This allows relatively cold water to flow into the inlet opening  270  through the second valve member  242  and to the outlet opening  272  for mixing with the relatively hot water flowing through the inlet  218 . As the second valve member  242  moves in the first direction, the first valve member  240  moves away from the valve seat  250  allowing a higher flow of high temperature water through the first inlet passage  204 . However, movement of the second valve member  242  to allow the cold water inlet  220  to open more fully simultaneously restricts the flow of the relatively hot water through the inlet  218 . Thus, upon reaching the setpoint temperature, the first and second valve members simultaneously move to provide the mixing of the high and low temperature. 
     Conversely, when the thermostat element  232  is exposed to temperatures less than the user selected setpoint temperature, the wax or other material within the thermostat element  232  will contract. This contraction allows the biasing force of the spring  236  to move the second valve member  242  in a second direction within the mixing chamber  216  towards the housing wall  276 . This prevents the flow of relatively cold water through inlet  220  and the second valve member for mixing with the relatively hot water flowing through the inlet  218 . This movement of the second valve member restricts the cold water inlet  220  and at the same time allows the hot water inlet  218  to open more fully. Thus, the exemplary mixing valve  200  automatically and continually maintains the mixed outlet water temperature at the user selected setpoint temperature within the tolerances of the mixing valve. 
     As indicated previously, the exemplary mixing valve  200  is adapted to provide feedback to a consumer of a failure condition of the valve assembly  230 . In a failure condition, the second valve member  242  can be retained in one of the fully closed position ( FIG. 4 ) and the fully open position ( FIG. 6 ). The valve could also fail to move in some position between the two positions. The fully open position will provide significant cold water inlet and a reduction of hot water through open  218 . This results in a colder water outlet condition and feedback to the user is water below a set temperature at the desired flow rate. A failure in the fully closed position will allow hot water to flow only through orifice opening  260  at a reduced flow rate. Thus, user feedback is one of the limited flow of the high temperature water or a low temperature fluid flowing out of the third passage. Particularly, as shown in  FIG. 4 , the first valve member  240  is configured to allow only a limited flow of the high temperature water upon initial demand from the first inlet passage. This high temperature water flows through the inlet  218  and the outlet passage  208  into the outlet line  120 . If the second valve member  242  is retained in the closed position, for example by a build-up of hard water particulates within the mixing chamber  216 , the first valve member  240  will also remain in the closed position. The user will immediately recognize this failure condition by the low flow of relatively hot water through the outlet line  120 . Thus, the valve assembly  230  prevents a high flow rate of relatively hot water through the outlet passage  208  during the failure condition. As shown in  FIG. 6 , the second valve member  242  is retained in the open position. This prevents the flow of relatively hot water through the inlet  218 . The user will immediately recognize this failure condition by the flow of relatively cold water through the outlet line  120 . Thus, the valve assembly  230  provides user feedback of a failure condition by providing one of a limited flow of relatively hot water and a flow of low temperature water through the outlet line  120  of the water heater  100 , conditions which are readily recognizable by the user. 
     With reference to  FIGS. 7 and 8 , a mixing valve  300  according to another aspect of the present disclosure is schematically illustrated. Similar to mixing valve  200 , mixing valve  300  is adapted to provide feedback to a consumer of a failure condition. The mixing valve  300  comprises a housing  302  including first and second inlet passages  304 ,  306  and an outlet passage  308 . The housing  302  includes a mixing chamber  316  which has a relatively hot water inlet  318  in fluid communication with the first inlet passage  304 , a relatively cold water inlet  320  in fluid communication with the second inlet passage  306  and a mixed water outlet  322  in fluid communication with the outlet passage  308 . 
     The mixing valve  300  includes a wax motor or valve assembly  330  which is at least partially received within the mixing chamber  316 . The valve assembly  330  includes a thermostat element  332 , a valve body  334  actuatable by the thermostat element and a biasing member, such as a spring  336 . In this exemplary embodiment, the thermostat element  332  is generally cylindrically shaped and includes a bore  338  extending longitudinally therethrough. The valve body  334  is configured to deliver the limited flow of relatively hot water to the thermostat element  332  to heat the thermostat element to a user selected setpoint temperature and prevent a high flow rate of hot temperature fluid through the third passage  308  upon failure of the valve assembly  330 . 
     The valve body  334  is displaceable within the mixing chamber  316  under the influence of the thermostat element  332  to simultaneously regulate the flow of relatively hot water from the first inlet passage  304  and flow of relatively cold water from the second inlet passage  306  into the mixing chamber upon full demand. More particularly, the valve body  334  includes a first valve member  340  and a second valve member  342  which is operatively associated with or connected to the first valve member. In this manner, the second valve member  342  moves simultaneously with the first valve member  340 . The first valve member  340  is configured to allow only a limited flow of the high temperature water upon initial user demand from the first inlet passage  304 . The first valve member  340  includes a hollow stem  344  connected to the second valve member  342  and a valve member  346 . As shown, the valve member  346  is generally washer-shaped and connected to one end of the stem  344 . The valve member  346  is selectively engageable with a valve seat  350  formed in the first inlet passage  304 . The stem defines a passage  352  having a narrow inlet orifice  353  in communication with the outlet line  120  and an outlet in communication with the bore  338  of the thermostat element  332 . The narrow orifice  353  and passage  352  is dimensioned to allow a limited flow of the relatively hot water upon initial demand from the outlet line  120  through the bore  338  of the thermostat element  332  and through the outlet passage  308 . 
     The second valve member  342  is located at least partially within the mixing chamber  316  and is operatively associated with the thermostat element  332  and with the second inlet passage  306  for regulating flow of the relatively cold water flowing through the inlet line  112 . In a closed position ( FIG. 7 ), the second valve member  342  abuts a wall  376  of the housing  302  to limit or prevent the flow of relatively cold water through the second valve member and into the mixing chamber  316 . In an open position ( FIG. 8 ), the second valve member  342  is spaced from the wall  376  thereby allowing the flow of relatively cold water into the mixing chamber  316 . A seal, such as O-ring  380 , can be provided to prevent leaking of the relatively cold water into the mixing chamber. 
     As shown in  FIG. 7 , upon initial demand, the first valve member  340  and the second valve member  342  are in a closed position. The narrow orifice  353  communicates with passage  352  to provide for a low flow of relatively hot water through the mixing valve  300 . To heat the thermostat element to its selected setpoint temperature, a limited flow of the high temperature water from the passage  352  flows through the bore  338  of the thermostat element  332 . As shown in  FIG. 8 , in a normal operating condition (i.e., full demand), when the thermostat element  332  is exposed to the high temperature water, the wax or other material within the thermostat element is caused to expand. This expansion acts against the spring  336  allowing the second valve member  342  to move within the mixing chamber  316  away from the housing wall  376 . This allows relatively cold water to flow into the inlet opening  320  through the second valve member  342  and to the outlet opening  322 . In addition, the first valve member  340  moves away from the valve seat  350  thereby allowing a greater flow of relatively hot water to flow through passage  378  ( FIGS. 7-8 ) and through inlet  318  for introduction into the mixing chamber. In this way, the relatively cold water will mix with the relatively hot water flowing through the inlet  318  and the bore  338  of the thermostat element  332 . 
     As indicated previously, the exemplary mixing valve  300  is adapted to provide feedback to a consumer of a failure condition of the valve assembly  330 . For example, in a failure condition, the first and second valve members  340 ,  342  are maintained in the closed position ( FIG. 7 ), wherein user feedback is the limited flow of the high temperature water out of the third passage  308  that is provided through the narrow orifice  353 . The user will immediately recognize this failure condition by the low flow of relatively hot water through the outlet line  120 . Thus, the valve assembly  330  prevents a high flow rate of relatively hot water through the outlet passage  308  during the failure condition. 
     With reference now to  FIGS. 9 and 10 , a mixing valve  400  according to yet another aspect of the present disclosure is schematically illustrated. Details of mixing valve  400  are generally similar to mixing valve  300  described above, therefore, further description herein of many of the details is deemed unnecessary. To further facilitate the heating of thermostat element  332 , the wall  376  includes at least one opening or bore  410  to allow another limited flow of the high temperature water from the inlet passage  304  once the valve  346  has opened. In the depicted embodiment, the wall  376  includes a configuration of openings  410 . As shown in  FIG. 9 , upon initial demand, the first valve member  340  and the second valve member  342  are in a closed position. The passage  352  directs a low flow of relatively hot water through the thermostat element  332  when the first valve member  340  is open or closed. As shown in  FIG. 10 , in a normal operating condition (i.e., full demand), when the thermostat element  332  is exposed to the high temperature water, the wax or other material within the thermostat element is caused to expand. This expansion acts against the spring  336  causing the first and second valve members to move downwardly a distance determined by thermostatic element  332 . More particularly, the second valve member  342  moves within the mixing chamber  316  away from the housing wall  376 , allowing relatively cold water to flow into the inlet opening  320  through the second valve member  342 , and the first valve member  340  moves away from the valve seat  350  thereby allowing a greater flow of relatively hot water to flow through passage  378  and through inlet openings  410  for introduction into the mixing chamber. In this way, the relatively cold water will mix with the relatively hot water flowing through the inlet openings  410  and the bore  338  of the thermostat element  332   
     It will be appreciated that various of the above-disclosed and other features and functions, or alternatives thereof, may be desirably combined into many other different systems or applications. Also that various presently unforeseen or unanticipated alternatives, modifications, variations or improvements therein may be subsequently made by those skilled in the art which are also intended to be encompassed by the following claims.