Patent Abstract:
The invention includes a gas valve control circuit for a gas-fired appliance and a method of activating the gas valve in the gas-fired appliance. The control circuit includes a controller, a first control circuit, a second control circuit, a first relay and a second relay. The first relay is operable to close when a switch in the first control circuit is activated. The second relay is operable to close when a switch in the second control circuit is activated. A third relay can be closed in response to activation of the second control circuit. The gas valve operates when the first and second relay are closed. The method includes the acts of closing a plurality of relays based on activation of a plurality of control circuits.

Full Description:
RELATED APPLICATIONS  
       [0001]     This application claims priority to U.S. Application Ser. No. 60/538,808, filed on Jan. 23, 2004. The contents of U.S. Application Ser. No. 60/538,808 are hereby incorporated by reference. 
     
    
     FIELD OF THE INVENTION  
       [0002]     The invention relates to an apparatus, such as a boiler, and methods of controlling the apparatus.  
       BACKGROUND  
       [0003]     Boilers are used in numerous situations for providing heat and/or power. One example boiler is a gas-fired boiler used for heating one or more buildings.  
       SUMMARY  
       [0004]     One embodiment of the invention includes a method of activating a valve in a gas-fired appliance. The method includes the acts of closing a first relay, transmitting a first signal to a first valve control circuit and a second signal to a second valve control circuit, closing a second relay in response to activation of the first valve control circuit, and closing a third relay in response to activation of the second valve control circuit.  
         [0005]     In another embodiment, the invention includes a gas valve control circuit for controlling a gas valve of a gas-fired appliance. The circuit includes a controller, a first control circuit connected and being responsive to the controller, a second control circuit connected to the controller, the first control circuit and the second control circuit each including a switch, a first relay operable to close when the switch in the first control circuit is activated and zero or more other conditions occur, and a second relay operable to close when the switch in the second control circuit is activated and zero or more other conditions occur, and wherein the gas valve operates based on the first and second relays.  
         [0006]     In yet another embodiment, the invention includes a gas-fired appliance comprising a heat source, a gas valve control circuit, and a gas valve connected to the heat source and the gas valve control circuit, the gas valve operable to deliver a flammable fluid to the heat source when the first and second relays are activated. The gas valve control circuit includes a controller, a first control circuit connected to the controller, a second control circuit connected to the controller, the first control circuit and the second control circuit each including a switch, a first relay operable to close when the switch in the first control circuit is activated and zero or more other conditions occur, and a second relay operable to close when the switch in the second control circuit is activated and zero or more other conditions occur.  
         [0007]     While the above aspects are described in connection with a boiler, one or more of the aspects can be applied to other apparatus, such as other gas-fired apparatus (e.g., a gas-fired water heater). 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]      FIG. 1  is a schematic representation of a boiler.  
         [0009]      FIG. 2  is a schematic representation of one construction of a control system capable of being implement with the boiler of  FIG. 1 .  
         [0010]      FIG. 3  is a schematic representation of one construction of a controller capable of being implemented with the control system of  FIG. 2 .  
         [0011]      FIG. 4  is a partial electrical schematic/block diagram of a gas valve control circuit capable of controlling the gas valve shown in  FIG. 1 .  
         [0012]      FIG. 5  is a partial electrical schematic/block diagram of an igniter detect circuit capable of detecting the igniter shown in  FIG. 1 . 
     
    
     DETAILED DESCRIPTION  
       [0013]     Before any embodiments of the invention are explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the following drawings. The invention is capable of other embodiments and of being practiced or of being carried out in various ways. Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. The use of “including,” “comprising,” or “having” and variations thereof herein is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. Unless specified or limited otherwise, the terms “mounted,” “connected,” “supported,” and “coupled” and variations thereof are used broadly and encompass both direct and indirect mountings, connections, supports, and couplings. Further, “connected” and “coupled” are not restricted to physical or mechanical connections or couplings.  
         [0014]      FIG. 1  schematically shows a self-contained, gas-fired boiler  100 . The boiler  100  includes inlet and outlet tubes  105  and  110 , which receive and issue a fluid, respectively. While only one inlet tube and one outlet tube is shown, the number of tubes  105  and  110  can vary. The fluid can be heated as it flows through a heat exchanger  115 . A pump  120  can be used to promote fluid movement through the heat exchanger  115 . While only one pump  120  is shown, the number of pumps can vary. The heat exchanger  115  is heated, either directly or indirectly, by one or more burners  130  disposed in a combustion chamber  125 . Unless specified otherwise, the boiler  100  will be described below as having only one burner  130  or one stage of burners. The combustion chamber  125  receives air (or similar fluid) from an air intake  135 , and issues the heated air through a flue  140  or exhaust. A blower  145  and/or a powered vent  150  can be used to promote and/or restrict the airflow through the combustion chamber  125 . The number of blowers and vents can vary depending on the application.  
         [0015]     For the boiler shown in  FIG. 1 , one or more igniters  155  ignite the one or more burners  130 . However, in other constructions, a pilot light can be used to ignite the one or more burners  130 . The boiler  100  also includes one or more gas valves  160  that controllably provide a combustible gas to the burner  130  from an inlet gas tube  165 .  
         [0016]     As shown in  FIG. 2 , a control system  200  provides control of the boiler  100 . The control system  200  includes a controller  205 , one or more user/factory input devices  210 , one or more sensors, the blower  145  (or a circuit or controller that controls the blower), the powered vent  150  (or a circuit or controller that controls the powered vent), the pump  120  (or a circuit or controller that controls the pump), the igniter  155  (or a circuit or controller that controls the igniter), the gas valve  160  (or a circuit or controller that controls the gas valve), and one or more user/factory output devices  215 . Of course, the control system  200  can include other control elements and not all of the control elements are required. Additionally, some of the elements of the control system  200  can be implemented in other systems coupled to the boiler.  
         [0017]     The one or more user/factory input devices  210  provide an interface for data or information to be communicated (e.g., from a user) to the controller  205 . Example input devices  210  include one or more switches (e.g., dip switches, push-buttons, etc.), one or more dials or knobs, a keyboard or keypad, a touch screen, a pointing device (e.g., a mouse, a trackball), a storage device (e.g., a magnetic disc drive, a read/write CD-ROM, etc.), a server or other processing unit in communication with the controller  205 , etc. A specific example user input device is a user interface module  220  having a keypad (e.g., touch switches) for entering information or data (e.g., set point temperatures, window, etc.). The one or more user/factory output devices provide an interface for data or information to be communicated (e.g., to a user) from the controller  205 . Example output devices  215  includes a display, a storage device (e.g., a magnetic disc drive, a read/write CD-ROM, etc.), a server or other processing unit in communication with the controller  205 , a speaker, a printer, etc. A specific example user output device  220  is the user interface module  220  having a LCD display, a plurality of LEDs, and a speaker. Of course, other input and output devices  210  and  215  may be added or attached, and/or one or more of the input and output devices  210  and  215  may be incorporated in one device. It should also be understood, the input and/or output device(s)  210  and/or  215  can be combined with other external circuitry that may or may not be part of the control system  100 . For example and as will be discussed further below, the user interface module (UIM)  220  can receive input from a user, communicate output to the user, and include other circuitry, such as temperature sensors for sensing ambient temperatures (e.g., one or more thermostat temperatures).  
         [0018]     The sensors are coupled to the boiler  100  and provide information to the controller  205  in response to a signal or stimuli. The sensors include one or more temperature sensors or probes  225  (e.g., inlet temperature, outlet temperature, tank temperature, thermostat input, etc.), an emergency cutout (ECO) temperature probe  230 , one or more pressure sensors  235  (e.g., a blocked flue sensor, a powered-vent sensor, a blower-prover sensor, a low-gas sensor, a high-gas pressure sensor), one or more water-level sensors  240 , one or more water-flow sensors  245 , one or more gas valve sensors  250 , one or more igniter-current sensors  255 , one or more flame sensors  260 , an AC polarity sensor  270 , etc. Additional sensors can be added and not all of the above-listed sensors are required in all constructions. Further, the sensors can be directly coupled with other elements of the control system  200  such that a single communication path is provided for controlling the element and obtaining information from the coupled sensor. It should also be understood that the communication can be wire communication and/or wireless communication.  
         [0019]     The ECO  230  is a thermostat switch and is located inside a probe disposed in or near the outlet pipe  110 . The ECO  230  is a normally closed switch that opens if the probe is exposed to a temperature higher than a trip point of the probe. As will be discussed below, electrical power for the gas valve relay  160  is passed through the ECO  230 . When open, the relay will turn off, and in turn, will shut off the gas supply.  
         [0020]     In general, the controller receives inputs (data, signals, information, etc.) from the one or more sensors  225 - 265  and the one or more input devices (e.g., the user/factor input devices  210 , the UIM  220 , etc.); processes and/or analyzes the signals; and communicates the processed signals and/or outputs control signals, in response to the processed or analyzed signals, to the one or more output devices (e.g., the user/factor output devices  215 , the pump  120 , the blower  145 , the gas valve  160 , the igniter  155 , the powered vent  150 , and/or UIM  220 ). A more detailed schematic of one construction of the controller is shown in  FIG. 3 .  
         [0021]     The controller  205  includes a central control board (CCB)  300  that communicates with multiple secondary boards, which may or may not be part of the controller  205 . Example secondary boards include a user interface board (UIB)  305 , a power distribution board (PDB)  310 , a touch sensor board (TSB)  315 , and one or more flame control boards (FCB 2 -FCB 4 )  320 ,  325 , and  330 .  
         [0022]     The CCB  300  is the central controller of the control system  200 , and contains conditioning circuits, driver or control circuits, a long-term memory circuit(s) for storing data, DC power supplies, an internal communication circuit, and two communication ports. The CCB  300  includes a master control section (MCS)  335  and a flame control section (FCB 1 )  340 . The MCS  335  includes a MCS microcontroller, and the FCB 1  section includes a FCB 1  microcontroller and a silicon-nitride (Si3N4) microcontroller. In one construction, the MCS microcontroller is a Microchip brand PIC18F6620-I/PT microcontroller, the FCB 1  microcontroller is an Atmel brand AT89C55WD-24JI microcontroller, and the Si3N4 microcontroller is a Microchip brand PIC16F876-20I/SO microcontroller. The Si3N4 microcontroller connects to a Si3N4 igniter (discussed further below) to operate the Si3N4 igniter. Each microcontroller includes an analog-to-digital converter, a processing unit (e.g., a microprocessor), and a memory. The memory includes one or more software modules (which may also be referred to herein as software blocks) having instructions. The processing unit obtains, interprets, and executes the instructions to perform processes.  
         [0023]     Each conditioning circuit receives input signal(s) from the one or more input devices (e.g., sensors) and conditions the input signal(s) to the proper voltage and/or current range for an attached microcontroller (e.g., the MCS microcontroller, the FCB 1  microcontroller, etc.). Each driver or control circuit receives output(s) from one or more microcontrollers and controls an attached output device (e.g., pump, blower, etc.) using the received output signal. The board communication circuit and the internal and external ports promote internal and external communications, respectively. The internal communication port connects to internal communication ports of the other control modules (e.g., the UIM  220 , the FCBs  320 ,  325 , and  330 ) using an RS-485 communication bus, thereby providing an internal communication network. The external communication port (also known as the network port) can be used to connect the control system  200  to a personal computer, a building automation system, a local area network, the Internet, a modem, or the like.  
         [0024]     The MCS microcontroller controls the overall operation of the boiler. This includes controlling the heating process, including the steps of receiving inputs from the one or more sensors, sending calls for heat to the FCB microcontroller(s), and sending calls for idle to the FCB microcontroller(s) once the heat has been satisfied. The MCS microcontroller also controls the powered vent and the pump, and provides a safety control for the gas valve.  
         [0025]     In response to control signals from the MCS microcontroller, the FCB microcontroller(s) executes a software program resulting in the control of the flame. The FCB controls the blower, gas valve, and igniter. For a Si3N4 igniter, the FCB provides an output to the Si3N4 microcontroller when activating the igniter. Once the igniter is lit, the Si3N4 microcontroller returns a signal to the FCB microcontroller informing the FCB of the operation. Other communication from the Si3N4 microcontroller to the FCB microcontroller includes error codes.  
         [0026]     The FCB 1   340  has one stage of combustion and flame safety control, and includes blower control, igniter control, and flame-detect circuitry. As additional safety checks, the gas relay output, igniter current, and blower outputs are monitored. For a multiple stage boiler, a separate flame control board (e.g., FCB 2 , FCB 3 , or FCB 4 ) is used for each stage. Each flame control board includes a FCB microcontroller, conditioning circuitry, control or driver circuitry, internal communication circuitry, and a Si3N4 microcontroller. Each FCB controls a respective blower, gas valve, and igniter, and includes an internal communication port for communicating with the MCS  335 .  
         [0027]     The use of multiple boards and microcontrollers allow for the modularity of the construction shown in  FIG. 3 . However, other constructions are possible. For example, the functionality of the separate flame control boards  320 ,  325 , and  330  can be combined with the FCB 1   340 , resulting in a single FCB microcontroller controlling all stages of combustion. As another example, a single processing unit can be used for the controller  205 .  
         [0028]     The UIM  220  allows full setup and operation of the boiler. The UIM  220  includes a housing that supports the UIB  305 , the TSB  315 , a LCD display, LED indicators, and touch switches. The UIB 305  provides means to both send and receive information to and from the user. The UIB  305  communicates with the CCB  300  and controls the operation of the LCD. The UIB 305  also receives inputs from the touch switches, and activates the LEDs according to signals provided by the CCB  300 . The TSB  315  includes the switch pads for the UIM  220  and provides inputs to the UIB 305 . The LEDs indicate the status of the boiler (e.g., running (Green), standby (Yellow), and service (Red), etc.).  
         [0029]     The PDB  310  distributes 120 VAC and 24 VAC power to the CCB  300  and the FCBs  320 ,  325 , and  330 . The PDB  310  also provides fusing for the control system  200  and a test circuit for determining if line power is properly applied to the system.  
         [0030]     The hardware is controlled by software that is embedded in the microcontrollers. For the construction shown in  FIG. 3 , four different software programs provide system control: a master control software program for the CCB microcontroller, a flame control software program for the FCB microcontroller(s), a user interface software program for the UIB microcontroller, and a Si3N4 software program for the Si3N4 microcontroller. These microcontrollers communicate with each other over the internal network.  
         [0031]     As was discussed earlier, the ECO  230  is a thermostat switch, which is located inside a probe disposed in or near the outlet pipe  110 . The ECO  230  is a normally closed switch that opens if the probe is exposed to a temperature higher than a trip point of the probe. Electrical power for the gas valve  160  passes through a relay controlled by the current flowing through the ECO  230 . When the ECO  230  opens, the ECO-controlled relay will in turn open, thereby de-energizing the gas valve  160 . The ECO  230  and the ECO-controlled relay perform a safety function. If the water temperature gets too hot, the opening of the ECO  230  will automatically override all of the other circuitry and shut off the power to the gas valve  160 . Software cannot de-bounce this physical action and the status of the ECO  230  is also passed to the MCS microcontroller.  
         [0032]     In some constructions of the control system  200 , additional relays can be added to control the operation of the gas valve  160 . The redundancy of the relays reduces the possibility of a component failure accidentally turning on the gas valve  160  at an improper time. One example construction of a circuit  400  for controlling operation of the gas valve  130  is shown in  FIG. 4 .  
         [0033]     With reference to the construction of the gas valve control circuit  400  shown in  FIG. 4 , the gas valve power is routed through three separate relay contacts. All three relays K 1 , K 2 , and K 3  are normally open and must be closed at the same time in order to route power to the valve  160 . Relay K 1 , which is the ECO-controlled relay, is the first relay in the string. Similar to what was previously discussed, the contacts of relay K 1  are closed when the ECO (Emergency Cut Out switch) is closed. If the ECO  230  is still open when the microcontroller  405  tries to turn on the gas valve  160 , the microcontroller  405  identifies a problem due to a lack of feedback from the signal conditioner  410 . The controller  205  can then declare a fault and inform the user of the problem via the UIM  230 . If the ECO contacts are closed when the microcontroller  405  attempts to open the gas valve  160 , the relay-control circuits  415  and  420  then control whether the valve  160  opens.  
         [0034]     The relay-control circuits  415  and  420  are connected to the microcontroller  405 , which for the controller shown in  FIG. 3  is one of the FCB microcontrollers, and are used to activate relays K 2  and K 3 , respectively. The microcontroller  405  includes multiple outputs GAS 1  and GAS 2  to prevent a problem of one output or port from affecting both relays K 2  and K 3 . Since the relay-control circuits  415  and  420  shown in  FIG. 4  are identical, only relay-control circuit  415  will be discussed in detail.  
         [0035]     With reference to  FIG. 4 , relay-control circuit  415  includes a one-shot multivibrator U 1 A, a transistor Q 1 , resistors R 1  and R 3 , and a capacitor C 1 . The output signal GAS 1  is a pulsing signal when active. The pulsing signal is pulsed at a set frequency to control the one-shot multivibrator U 1 A. In order to activate the one-shot multivibrator U 1 A, the pulsing signal should have repetitive transitions from high to low in approximately less time than the effective pulse width (or time constant) of circuit R 1 , C 1 , which is applied to the one-shot multivibrator U 1 A. If the transitions are faster than the effective pulse width of the circuit R 1 , C 1 , the Q output of the multivibrator U 1 A goes high and turns on the transistor Q 1 . The activating of the transistor Q 1  activates the relay K 2 . If the transition is slower than the pulse width of the circuit R 1 , C 1  or some pulses are missed, the Q output of the multivibrator U 1 A goes low and turns off the switch Q 1 . The deactivating of the transistor Q 1  deactivates the relay K 2 . The resistor R 3  limits the current through the switch Q 1 , and the diode D 1  reduces the “kick-back” voltage on the coil of the relay K 2  when the relay is deactivated. In addition to providing the proper pulsing signals GAS 1  and GAS 2 , the microcontroller  405  also drives the ENABLE signal low to turn on the relays K 2  and K 3 .  
         [0036]     In order for the gas valve  160  to open, all three relays K 1 , K 2 , and K 3  need to be closed at the same time. That is, the outlet water temperature must be less than the set point of the ECO  230 , the microcontroller  405  must pulse the signals GAS 1  and GAS 2  at approximately the proper rate, and the Enable line be pulled low to close both of the relays K 2  and K 3 . If any of these conditions are not met, the gas valve  160  will not operate.  
         [0037]     Further, control of the gas valve  160  can occur even if one of the relays K 2  or K 3  shorts. For example, if relay K 3  shorts, relay K 2  would still provide control of the gas valve  160 , including turning the gas valve  160  off.  
         [0038]     Again with reference to  FIG. 4 , the microcontroller  405  also monitors the signal FEEDBACK to know when power is being applied to the gas valve  160 . By comparing the signal FEEDBACK to the requested output, the microcontroller  405  can declare a fault if the microcontroller  405  detects a problem. For example, a fault can be declared if power is not properly applied to the gas valve  160  when commanded, or power is applied to the gas valve  160  when not commanded. For a specific example, if the contacts of both relays K 2  and K 3  are shorted, power can be applied to the gas valve  160  irrespective of whether the valve  160  is to be opened or closed. The microcontroller  405  detects if power is erroneously provided to the gas valve  160  by the signal FEEDBACK and declares a fault to the user. If the user does not respond to the fault, the gas valve  160  remains on until the outlet water reaches the ECO thermostat temperature. This deactivates relay K 1 , which closes the gas valve  160 .  
         [0039]     Before proceeding further, it should be noted that while the control circuit  400  was described as controlling the gas valve  160 , the circuit  400  can control other valves or apparatus. Additionally, while the circuit was described with the relay-control circuits  415  and  420 , other circuits can be used for controlling relays K 2  and K 3 .  
         [0040]     As discussed earlier with reference to  FIG. 1 , the boiler  100  includes an igniter  155  to ignite the burner  130 . In one construction, the igniter  155  comprises a silicon-carbide (SiC) material, and in another construction, the igniter  155  comprises a silicon-nitride (Si3N4) material. In some constructions of the control system  200 , the system  200  allows either material to be used as the igniter  155 . Furthermore, for these constructions, the controller  205  can automatically determine the type of igniter  155  connected to the controller  205 . One example construction of a circuit  500  for detecting the igniter type connected to the controller  205  is shown in  FIG. 5 .  
         [0041]     With reference to  FIG. 5 , either a SiC igniter  505  or a Si3N4 igniter  510  connects to the controller  515  and is used for igniting the burner  130 . The igniter  505  or  510  can be installed at the factory or installed “on-location” by a service technician. The microcontroller  515  can be one of the FCB microcontrollers described in connection with  FIG. 3 .  
         [0042]     As shown in  FIG. 5 , the SiC igniter  505  lights the burner  130  when the signal IGNITER causes relay K 1  to close. A conventional current proving circuit  520  monitors the current through the igniter  505  to insure that the igniter  505  has sufficient current to produce ignition temperature. When the current exceeds a set value, the circuit  520  provides a signal to microcontroller  515  indicating that the igniter is on. The set point can be set using jumpers and can depend on the manufacturer of the SiC igniter  505 .  
         [0043]     With reference again to  FIG. 5 , a Si3N4 microcontroller and control circuit  525  controls the Si3N4 igniter  510 . An exemplary Si3N4 microcontroller  525  is distributed by White-Rodgers, at http://www.white-rodgers.com, as part no. 21D64-100E1. An exemplary control circuit for controlling the Si3N4 igniter is disclosed in U.S. Pat. No. 6,521,869, which is incorporated herein by reference. When activating the Si3N4 igniter, the signal IGNITER is driven low to turn on K 1  and apply power to triac Q 1 . A short time later, a “go” signal is communicated to the Si3N4 microcontroller  525 . The Si3N4 microcontroller and control circuit  525  ignites the Si3N4 igniter  510  in response to the “go” signal, by activating triac Q 1 . If ignition is successful, a successful result is communicated (on the “Proven” line) from the Si3N4 microcontroller  525  to the microcontroller  515 . If a fault occurs, the fault is communicated from the Si3N4 microcontroller  525  to the microcontroller  515 . The signal FAULT provides fault information to the microcontroller  515  and allows microcontroller  515  to clear the fault condition(s). In a different construction, the triac Q 1  is directly connected to line power such that the relay K 1  is not required.  
         [0044]     When attempting to activate the igniter for the first time after a power-up, the controller  515  automatically determines the type of igniter installed on each stage of the boiler  100  (if more than one stage). Of course, the determination can be made at a different time. The determination can be made similarly for each stage, so only one stage will be explicitly discussed herein.  
         [0045]     In one method, the microcontroller  515  first attempts activating the SiC igniter as discussed above. The microcontroller  515  then monitors the signal FEEDBACK from the current sensing circuit  520  to determine whether a positive result occurs at anytime up to when the Si3N4 returns a positive “Proven” feedback. If the result is positive, the microcontroller  515  stores the result in memory. After a short time period, the microcontroller  515  then provides a “go” signal to the Si3N4 microcontroller and control circuit  525 . The microcontroller  515  then monitors whether a positive reply is provided back from the Si3N4 microcontroller  525  within a time period. If a positive feedback is received from the current sensing circuit  520  at any time before a positive “Proven” feedback is received, the “Go” signal is removed to stop the Si3N4 process. If the result is positive, the microcontroller  515  stores the result in memory. If a positive feedback is not received, the controller  205  stops the igniter process and declares an error. The detected type of igniter is stored in memory, and all subsequent operations will only activate the detected type until cycling power clears the memory. Of course, the order of the steps of the just discussed method can vary and other methods are possible.  
         [0046]     As an alternative method, the microcontroller  515  provides an activation signal to both the SiC igniter control circuit and the Si3N4 igniter control circuit at substantially the same time. The microcontroller  515  activates the SiC circuitry by enabling the output line IGNITER and activates the Si3N4 circuitry by enabling the output line GO. Feedback signals from both the current sensing circuit  510  and the Si3N4 microcontroller are then monitored to determine which igniter is installed. If a positive result is received from the current sensing circuit, the microcontroller  515  knows that the stage has a SiC igniter  505  and activation of the Si3N4 igniter  510  is no longer needed. The system would then cancel the “go” command to the Si3N4 control circuit. If no current feedback is seen in a time period, then the microcontroller  515  waits for feedback from the Si3N4 microcontroller. If the Si3N4 microcontroller  515  completes its ignition sequence and returns a positive result, then a Si3N4 igniter  510  is coupled to the controller  205 . The detected type of igniter is stored in memory, and all subsequent operations will only activate the detected type until cycling power clears the memory. If the feedback indicates that neither of the igniters is connected then a fault is declared. If both types of igniters are installed, the microcontroller can use one type of igniter for all subsequent operations and ignore the other.  
         [0047]     In yet another method, the microcontroller  515  first attempts activating the Si3N4 igniter as discussed above. The microcontroller  515  then monitors the signal FEEDBACK from the current sensing circuit  520  to determine whether a positive result occurs within a time period. If the result is positive, the microcontroller  515  stores the result in memory. If not, the microcontroller  515  then provides a “go” signal to the Si3N4 microcontroller and control circuit  525 . The microcontroller  525  then monitors whether a positive reply is provided back from the Si3N4 microcontroller within a time period. If the result is positive, the microcontroller  515  stores the result in memory. If not, the controller  205  indicates an error has occurred. The detected type of igniter is stored in memory, and all subsequent operations will only activate the detected type until cycling power clears the memory. Of course, the order of the steps of the just discussed method can vary (e.g., the microcontroller tests for a Si3N4 igniter first) and other methods are possible.  
         [0048]     As was discussed earlier with reference to  FIG. 2 , the control system  200  can include a user interface module (UIM)  220  that receives input from a user. The UIM  220  allows, among other things, full setup and operation of the boiler  100 . The setup can include one or more temperature set points (e.g., an operating set point, a high limit set point, etc.) and one or more temperature differentials (e.g., a temperature differential of one degree Celsius for a set point). The controller  205  uses the set point(s), the temperature differential(s), and sensed temperature information to control the boiler  100 .  
         [0049]     In one method of operation, the controller  205  operates in one of at least two states (a normal state and a short-cycling-prevention state) and each state has at least two modes (a running mode, where the heating sequence is active, and a standby mode, where no heat is needed). When in the normal state, the boiler  100  operates as set or programmed by the user. When in the short-cycling-prevention state, the boiler  100  adjusts operation of the boiler  100  such that the controller  205  does not strictly follow the settings created by the user (i.e., modifies the normal state). Of course, other states and modes can be added (e.g., an error state, a vacation or sleep state), and the descriptors used for each state and mode (e.g., “normal” state, “running” mode, etc.) are only meant as example descriptors (e.g., the “normal” state can alternatively be referred to as the “standard” state or variations thereof). It should also be understood that the short-cycling-prevention state can modify other states and not just the normal state as discussed herein.  
         [0050]     The term “short-cycling condition” is referred to herein as a condition where the boiler  100  performs at a rapid cycling rate, each cycle including the activation and deactivation of the burner  130 . For example and in one construction, the boiler  100  is in a short-cycling condition when one or more stages of the boiler  100  performs thirty cycles in one hour. A short-cycling condition can occur, for example, when the temperature differential is set too tight. Short cycling increases the number of cycles performed by the boiler  100 , and can lead to premature failure of one or more components of the boiler  100 .  
         [0051]     The short-cycling-prevention state affects the operation of the standby and/or running modes. For example, the short-cycling-prevention state can adjust one or more set values to a default value (e.g., automatically change the temperature differential to three degrees Celsius, change a temperature set-point, etc.), can adjust a set value (e.g., increase the temperature differential of the normal state by one degree Celsius/hour until the short cycling condition ceases), and/or can force a minimum amount of time to elapse before allowing cycling to occur (e.g., delay a call for heat for a minimum of at least 180 seconds after the last call for heat). One result of the short-cycling-prevention state is the delaying of one or more cycles such that the number of cycles in a time period is reduced.  
         [0052]     For one construction, the controller  205  issues an alarm informing the user that a short-cycling condition occurred when the controller  205  enters the short-cycling-prevention state. For this construction, the controller  205  stays in the short-cycling-prevention state until the user acknowledges the condition. In another construction, the controller  205  operates in the short-cycling-prevention state for a time period upon detecting the short-cycling condition. After the time period has lapsed, the controller  205  returns to the normal state (or other applicable state) to determine whether the condition causing the short-cycling has resolved itself. If not, then the controller  205  will re-enter the short-cycling-prevention state and an alarm will occur. Other variations are envisioned.  
         [0053]     It should also be noted that the short-cycling-prevention state can be independently determined and controlled for each heating stage. Alternatively, the short-cycling-prevention state for each of the heating stages can be related. For example and in one method, if the short cycling-prevention state was entered while the system was in idle, then the next transition to the heating sequence for stage1 will not be allowed for 180 seconds. Then, when the sequence reaches the end of the heating sequence for stage1, the controller  205  will wait 180 seconds before entering the heating sequence for stage 2, and so on.  
         [0054]     While the invention has been described in connection with the self-contained, gas-fired boiler, the invention can be used in other boiler types. Additionally, it is contemplated that aspects of the invention can be used with other appliances (e.g., a gas-fired appliance such as a water heater).  
         [0055]     Various features and advantages of the invention are set forth in the following claims.

Technology Classification (CPC): 5