Patent Publication Number: US-11655584-B2

Title: Dryer appliance nuisance trip detection

Description:
FIELD OF THE INVENTION 
     The present subject matter relates generally to dryer appliances, and more particularly to dryer appliances configured for detecting when a heating system of the dryer appliance is not operating, such as due to a nuisance trip or heater failure, and related methods. 
     BACKGROUND OF THE INVENTION 
     A conventional appliance for drying articles such as a clothes dryer (or laundry dryer) for drying clothing articles typically includes a cabinet having a rotating drum for tumbling clothes and laundry articles therein. One or more heating elements, for example electric heating elements, heat air prior to the air entering the drum, and the warm air is circulated through the drum as the clothes are tumbled to remove moisture from laundry articles in the drum. 
     In order to avoid excessive heating of articles within the drum, dryer appliances include one or more heat control systems which measure or monitor temperatures within the dryer appliance and deactivate the one or more heating elements in response to the temperatures exceeding predetermined thresholds. For example, the one or more heat control systems may include one or more thermostats which trip, or open a circuit to interrupt a supply of electrical power, at one or more respective temperature thresholds. 
     When one or more such thermostats trip, it or they must reset before the dryer appliance can resume operation. The time for the reset increases the overall time duration of the drying operation. Thus, it is desirable to minimize or avoid tripping the thermostats. In particular, it is desirable to minimize or avoid tripping of the thermostats due to a false positive or other nuisance tripping of the thermostats. 
     Accordingly, a dryer appliance having improved heat control systems and improved methods of determining status of the heating systems would be advantageous. 
     BRIEF DESCRIPTION OF THE INVENTION 
     Aspects and advantages of the invention will be set forth in part in the following description, or may be obvious from the description, or may be learned through practice of the invention. 
     In one exemplary aspect of the present disclosure, a dryer appliance is provided. The dryer appliance includes a cabinet with a drum rotatably mounted within the cabinet. The drum defines a chamber for the receipt of articles for drying. The dryer appliance also includes a heating system fluidly coupled to the drum whereby heated air flows from the heating system to the chamber of the drum for drying of articles within the chamber. The dryer appliance further includes a primary heat control system comprising a thermistor and a secondary heat control system comprising a thermostat. The dryer appliance also includes a controller in operative communication with the thermistor of the primary heat control system. The controller is configured to monitor a temperature with the thermistor of the primary heat control system. The controller is also configured to determine a temperature gradient of the monitored temperature based on a rate of change in the monitored temperature over time. When the temperature gradient changes from positive to negative, the controller is configured to store a current value of the monitored temperature as a peak temperature. After a first wait period has elapsed, the controller is further configured to verify the temperature gradient is still negative. After verifying the temperature gradient is still negative after the first wait period, the controller is configured to verify there is a call for heating. The controller is also configured to allow a second wait period to elapse after verifying the call for heating. After the second wait period, the controller is configured to verify the temperature gradient is still negative. After verifying the temperature gradient is still negative after the second wait period, the controller is configured to store a present value of the monitored temperature. The controller is further configured to determine that a difference between the peak value of the monitored temperature and the present value of the monitored temperature is greater than a predetermined threshold. The controller is also configured to detect a nuisance trip because the difference between the peak value of the monitored temperature and the present value of the monitored temperature is greater than the predetermined threshold. 
     In another exemplary aspect of the present disclosure, a method of operating a dryer appliance is provided. The method includes monitoring a temperature with a thermistor of a primary heat control system of the dryer appliance and determining a temperature gradient of the monitored temperature based on a rate of change in the monitored temperature over time. When the temperature gradient changes from positive to negative, the method includes storing a peak value of the monitored temperature. After a first wait period, the method includes verifying the temperature gradient is still negative. After verifying the temperature gradient is still negative, the method includes verifying there is a call for heating. After verifying the call for heating, the method includes allowing a second wait period to elapse. After the second wait period, the method includes verifying the temperature gradient is still negative. After verifying the temperature gradient is still negative, the method includes storing a present value of the monitored temperature. The method also includes determining that a difference between the peak value of the monitored temperature and the present value of the monitored temperature is greater than a predetermined threshold. The method further includes detecting a nuisance trip because the difference between the peak value of the monitored temperature and the present value of the monitored temperature is greater than the predetermined threshold. 
     In yet another exemplary aspect of the present disclosure, a method of operating a dryer appliance is provided. The method includes monitoring a temperature with a thermistor of a primary heat control system of the dryer appliance. The method also includes determining a relay signal is calling to close a relay and thereby activate a heating system of the dryer appliance and verifying that the relay is closed. The method further includes allowing a minimum relay on time to elapse after verifying that the relay is closed. The method also includes determining a temperature gradient of the monitored temperature based on a change in the monitored temperature over the minimum relay on time. The method further includes detecting a nuisance trip because the determined temperature gradient is negative. 
     These and other features, aspects, and advantages of the present disclosure will become better understood with reference to the following description and appended claims. The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the disclosure and, together with the description, serve to explain the principles of the disclosure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A full and enabling disclosure of the present invention, including the best mode thereof, directed to one of ordinary skill in the art, is set forth in the specification, which makes reference to the appended figures. 
         FIG.  1    provides a perspective view of a dryer appliance in accordance with exemplary embodiments of the present disclosure. 
         FIG.  2    provides a perspective view of the example dryer appliance of  FIG.  1    with portions of a cabinet of the dryer appliance removed to reveal certain components of the dryer appliance. 
         FIG.  3    provides a flow chart of an exemplary method of operating a dryer appliance according to one or more embodiments of the present disclosure. 
         FIG.  4    provides a flow chart of another exemplary method of operating a dryer appliance according to one or more embodiments of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     Reference now will be made in detail to embodiments of the invention, one or more examples of which are illustrated in the drawings. Each example is provided by way of explanation of the invention, not limitation of the invention. In fact, it will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the scope or spirit of the invention. For instance, features illustrated or described as part of one embodiment can be used with another embodiment to yield a still further embodiment. Thus, it is intended that the present invention covers such modifications and variations as come within the scope of the appended claims and their equivalents. 
     As used herein, terms of approximation, such as “generally,” or “about” include values within ten percent greater or less than the stated value. When used in the context of an angle or direction, such terms include within ten degrees greater or less than the stated angle or direction. For example, “generally vertical” includes directions within ten degrees of vertical in any direction, e.g., clockwise or counter-clockwise. 
     Turning now to the figures,  FIG.  1    provides a perspective view of dryer appliance  10  according to one or more exemplary embodiments of the present disclosure.  FIG.  2    provides another perspective view of dryer appliance  10  with a portion of a cabinet or housing  12  of dryer appliance  10  removed in order to show certain components of dryer appliance  10 . Dryer appliance  10  generally defines a vertical direction V, a lateral direction L, and a transverse direction T, each of which is mutually perpendicular, such that an orthogonal coordinate system is defined. While described in the context of a specific embodiment of dryer appliance  10 , using the teachings disclosed herein, it will be understood that dryer appliance  10  is provided by way of example only. Other dryer appliances having different appearances and different features may also be utilized with the present subject matter as well. 
     Cabinet  12  includes a front panel  14 , a rear panel  16 , a pair of side panels  18  and  20  spaced apart from each other by front and rear panels  14  and  16 , a bottom panel  22 , and a top cover  24 . Within cabinet  12 , an interior volume  29  is defined. A drum or container  26  is mounted for rotation about a substantially horizontal axis within the interior volume  29 . Drum  26  defines a chamber  25  for receipt of articles of clothing for tumbling and/or drying. Drum  26  extends between a front portion  37  and a back portion  38 . Drum  26  also includes a back or rear wall  34 , e.g., at back portion  38  of drum  26 . A supply duct  41  may be mounted to rear wall  34  and receives heated air that has been heated by a heating assembly or system  40 . 
     As used herein, the terms “clothing” or “articles” includes but need not be limited to fabrics, textiles, garments, linens, papers, or other items from which the extraction of moisture is desirable. Furthermore, the term “load” or “laundry load” refers to the combination of clothing that may be washed together in a washing machine or dried together in a dryer appliance  10  (e.g., clothes dryer) and may include a mixture of different or similar articles of clothing of different or similar types and kinds of fabrics, textiles, garments and linens within a particular laundering process. 
     A motor  31  is provided in some embodiments to rotate drum  26  about the horizontal axis, e.g., via a pulley and a belt (not pictured). Drum  26  is generally cylindrical in shape, having an outer cylindrical wall  28  and a front flange or wall  30  that defines an opening  32  of drum  26 , e.g., at front portion  37  of drum  26 , for loading and unloading of articles into and out of chamber  25  of drum  26 . A plurality of lifters or baffles  27  are provided within chamber  25  of drum  26  to lift articles therein and then allow such articles to tumble back to a bottom of drum  26  as drum  26  rotates. Baffles  27  may be mounted to drum  26  such that baffles  27  rotate with drum  26  during operation of dryer appliance  10 . 
     Drum  26  includes a rear wall  34  rotatably supported within main housing  12  by a suitable fixed bearing. Rear wall  34  can be fixed or can be rotatable. Rear wall  34  may include, for instance, a plurality of holes that receive hot air that has been heated by a heating assembly or system  40 , as will be described further below. Motor  31  is also in mechanical communication with an air handler  48  such that motor  31  rotates a fan  49 , e.g., a centrifugal fan, of air handler  48 . Air handler  48  is configured for drawing air through chamber  25  of drum  26 , e.g., in order to dry articles located therein. In alternative example embodiments, dryer appliance  10  may include an additional motor (not shown) for rotating fan  49  of air handler  48  independently of drum  26 . 
     Drum  26  is configured to receive heated air that has been heated by a heating assembly  40 , e.g., via holes in the rear wall  34  as mentioned above, in order to dry damp articles disposed within chamber  25  of drum  26 . For example, heating assembly  40  may include a heating element (not shown), such as a gas burner, an electrical resistance heating element, or heat pump, for heating air. In particular embodiments, the heating assembly  40  may be or include an electric heater comprising a plurality of electric resistance heating elements with a plurality of relays for selectively providing or obstructing electrical power to the heating elements, such as two relays which permit operation of the heating assembly  40  at various power levels, such as 50% power when only one of two relays is closed. As discussed above, during operation of dryer appliance  10 , motor  31  rotates drum  26  and fan  49  of air handler  48  such that air handler  48  draws air through chamber  25  of drum  26  when motor  31  rotates fan  49 . In particular, ambient air enters heating assembly  40  via an inlet  51  due to air handler  48  urging such ambient air into inlet  51 . Such ambient air is heated within heating assembly  40  and exits heating assembly  40  as heated air. Air handler  48  draws such heated air through supply duct  41  to drum  26 . The heated air enters drum  26  through a plurality of outlets of supply duct  41  positioned at rear wall  34  of drum  26 . 
     Within chamber  25 , the heated air may accumulate moisture, e.g., from damp clothing disposed within chamber  25 . In turn, air handler  48  draws moisture-saturated air through a screen filter (not shown) which traps lint particles. Such moisture-statured air then enters an exit duct  46  and is passed through air handler  48  to an exhaust duct  52 . From exhaust duct  52 , such moisture-statured air passes out of dryer appliance  10  through a vent  53  defined by cabinet  12 . After the clothing articles have been dried, they are removed from the drum  26  via opening  32 . A door  33  ( FIG.  1   ) provides for closing or accessing drum  26  through opening  32 . The door  33  may be movable between an open position and a closed position, the open position for access to the chamber  25  defined in the drum  26 , and the closed position for sealingly enclosing the chamber  25  defined in the drum  26 . 
     In some embodiments, one or more selector inputs  70 , such as knobs, buttons, touchscreen interfaces, etc., may be provided or mounted on a cabinet  12  (e.g., on a backsplash  71  of the cabinet  12 ) and are in operable communication (e.g., electrically coupled or coupled through a wireless network band) with a processing device or controller  100 . A display  56  may also be provided on the backsplash  71  and may also be in operable communication with the controller  100 . Controller  100  may also be provided in operable communication with motor  31 , air handler  48 , and/or heating assembly  40 . In turn, signals generated in controller  100  direct operation of motor  31 , air handler  48 , and/or heating assembly  40  in response to the position of inputs  70 . In the example illustrated in  FIG.  2   , the inputs  70  are provided as knobs. In other embodiments, inputs  70  may also or instead include buttons, switches, touchpads and/or a touch screen type interface. 
     Controller  100  is a “processing device” or “controller” and may be embodied as described herein. As used herein, “processing device” or “controller” may refer to one or more microprocessors, microcontrollers, application-specific integrated circuits (ASICS), or semiconductor devices and is not restricted necessarily to a single element. The controller  100  may be programmed to operate dryer appliance  10  by executing instructions stored in memory (e.g., non-transitory media). The controller  100  may include, or be associated with, one or more memory elements such as RAM, ROM, or electrically erasable, programmable read only memory (EEPROM). For example, the instructions may be software or any set of instructions that when executed by the processing device, cause the processing device to perform operations. Controller  100  may include one or more processor(s) and associated memory device(s) configured to perform a variety of computer-implemented functions and/or instructions (e.g. performing the methods, steps, calculations and the like and storing relevant data as disclosed herein). It should be noted that controllers as disclosed herein are capable of and may be operable to perform any methods and associated method steps as disclosed herein. For example, in some embodiments, methods disclosed herein may be embodied in programming instructions stored in the memory and executed by the controller. 
     In some exemplary embodiments, the dryer appliance  10  may include one or more temperature sensors, such as inlet temperature sensor  43  and/or outlet temperature sensor  47 . The temperature sensor(s) may be in operative communication with the controller  100 . For example, in various embodiments, the controller  100  may be operable to detect, measure, and/or monitor one or more temperatures within the dryer appliance  10 . Such temperatures which may be detected, measured, and/or monitored include, for example, an inlet temperature measured with the inlet temperature sensor  43  and/or an outlet temperature measured with the outlet temperature sensor  47 . The temperature sensors  43  and  47  may be, in some embodiments, thermistors. 
     The temperature sensors  43  and  47  may be part of a primary heat control system of the dryer appliance  10 . The dryer appliance  10  may also include a secondary or backup heat control system including one or more thermostats. When either the primary heat control system or the second heat control system (or both) detects excessive heat, e.g., a temperature above a threshold or limit value, which may be an instantaneous temperature or a temperature exceeding the limit for a minimum period of time, the heating assembly  40  may be deactivated until the respective heat control system resets. As will be recognized by those of ordinary skill in the dryer art, the thermostats of the secondary heat control system generally take longer to reset after detecting excessive heat. Thus, the secondary heat control system may be set to a higher temperature threshold value or temperature limit in order to reduce or avoid tripping the secondary heat control system and thus reduce or avoid the relatively longer (as compared to the thermistors of the primary heat control system) reset time of the thermostat(s) in the secondary heat control system. 
     In some instances, the secondary heat control system may experience a nuisance trip, when one or more, e.g., both, thermostats in the secondary heat control system trip and deactivate, e.g., cut off electric power from, the heating assembly  40 . 
       FIG.  3    provides a flow chart of an exemplary method  200  of operating a dryer appliance according to one or more additional embodiments of the present disclosure. Method  200  may begin with an initial step  202  of monitoring a temperature with a thermistor of a primary heat control system of the dryer appliance. For example, the thermistor may be an inlet thermistor and the temperature may be a temperature within the inlet duct of the dryer appliance. As another example, the thermistor may be an outlet thermistor and the temperature may be a temperature within the outlet duct of the dryer appliance. Monitoring the temperature may include continuously measuring or detecting the temperature or measuring the temperature repeatedly at predetermined intervals, such as every second or twice per second, etc. 
     As shown at  204  in  FIG.  3   , the method  200  may also include determining a temperature gradient of the monitored temperature based on a rate of change in the monitored temperature over time. For example, the temperature gradient may be a slope of the temperature over time. A positive temperature gradient may correspond to increasing temperature, whereas a negative temperature gradient may correspond to decreasing temperature. When the temperature gradient changes from positive to negative, e.g., when the slope of the temperature over time inflects because the temperature stops increasing and starts to decrease, the method  200  may include a step  206  of storing the current value of the temperature as a peak value of the temperature. 
     After storing the peak value of the temperature, the method  200  may then allow a first wait period to elapse. For example, as illustrated at step  208  in  FIG.  3   , the method  200  may include verifying that the temperature is still decreasing, e.g., verifying the temperature gradient is still negative, after the first wait period. In various embodiments, the first wait period may be between about one second and about ten seconds, such as between about two seconds and about seven seconds, such as about three seconds. 
     When the temperature has continued to decrease after the first wait period, the method  200  may also include verifying that there is a call for heating, e.g., as illustrated at step  210  in  FIG.  3   . Verifying the call for heating indicates that the negative temperature gradient, e.g., the decreasing temperature, was not caused by the primary heat control system or the controller turning off the heat. Verifying the call for heating may include verifying that at least one relay of the heating system is closed, such that electrical power is supplied to at least one heating element of the heating system but for the primary heat control system and/or secondary heat control system having tripped, in particular, verifying that there is a call for heating while the temperature is nonetheless continuing to decrease may confirm that the thermostat of the secondary heat control has tripped and is preventing activation of the heating element despite the closed relay. 
     In some embodiments, the method  200 , e.g., the step  210  of verifying the call for heating, may also include verifying that no relays were opened within a predetermined period of time, such as within the last about fifteen seconds. The predetermined period of time may, in various embodiments, be between about five seconds and about thirty-five seconds, such as between about ten seconds and about thirty seconds, such as between about fifteen seconds and about twenty-five seconds, such as about fifteen seconds, or about twenty seconds, or about twenty-five seconds. 
     When the temperature gradient is still negative at step  208  and there is a call for heating, e.g., no relays were opened within the predetermined period of time and/or at least one relay is closed, at step  210 , the method  200  may then include a second wait period. In various embodiments, the second wait period may be between about five seconds and about twenty-five seconds, such as between about ten seconds and about twenty seconds, such as about fifteen seconds. 
     In some embodiments, for example as illustrated at step  212  in  FIG.  3   , the method  200  may further include verifying that the temperature gradient is still negative after the second wait period. As illustrated in  FIG.  3   , the step  212  occurs after, and in at least some embodiments is performed because, the temperature gradient was negative after the first wait period, e.g., at step  208 , and the call for heating was verified, e.g., at step  210 . 
     In some embodiments, the monitored temperature may be an inlet temperature which is monitored with an inlet thermistor, e.g., a thermistor which is positioned upstream of the drum  26  and the chamber  25  defined therein with respect to the flow of heated air from the heating system  40 . For example, the inlet thermistor may be inlet temperature sensor  43  positioned in the supply duct  41 , e.g., as illustrated in  FIG.  2   . In embodiments where the monitored temperature is the inlet temperature, the method may also include measuring an outlet temperature and comparing the outlet temperature to one or more outlet temperature setpoints. For example, the outlet temperature may be a temperature value measured and/or monitored with a thermistor downstream of the drum  26  and the chamber  25  defined therein with respect to the flow of heated air from the heating system  40 , such as the outlet temperature sensor  47  positioned in the exhaust duct  52  and/or downstream of the air handler  48 , e.g., as illustrated in  FIG.  2   . Comparing the outlet temperature to one or more outlet temperature setpoints may be or include determining whether the outlet temperature is less than at least one minimum outlet upper setpoint. For example, in embodiments where more than one relay is included, the primary heat control system may include an upper and lower setpoint for each thermistor and each relay, e.g., four total setpoints in embodiments which include two thermistors (such as the inlet thermistor and the outlet thermistor) and two relays, such as the inlet thermistor may have a lower setpoint at which one relay is opened and an upper setpoint at which both relays are opened, while the outlet thermistor also has a lower setpoint at which one relay is opened and an upper setpoint at which both relays are opened. In particular embodiments, the setpoints may include a lower inlet setpoint and an upper inlet setpoint based on the inlet temperature measured or monitored with the inlet thermistor and a lower outlet setpoint and an upper outlet setpoint based on the outlet temperature measured or monitored with the outlet thermistor. The lower inlet setpoint and the lower outlet setpoint may control a first relay while the upper inlet setpoint and the upper outlet setpoint control a second relay. Thus, in some exemplary embodiments, the method  200  may include comparing the outlet temperature to both the upper outlet setpoint and the lower outlet setpoint, such as determining whether the outlet temperature is less than both the upper outlet setpoint and the lower outlet setpoint. This comparison may be useful to determine or verify that the operation of the heating system is inlet-controlled, e.g., that the heating system is activated (including partially activated, such as when only one of multiple relays is closed) or deactivated (i.e., when the heating system is not drawing power, although other components of the dryer appliance, such as the motor, may be drawing power) based on the inlet temperature rather than on the outlet temperature. 
     In some embodiments, the method  200  may include allowing a third wait period to elapse. In various embodiments, the third wait period may be between about five seconds and about twenty-five seconds, such as between about ten seconds and about twenty seconds, such as about fifteen seconds. Allowing the third wait period to elapse may be performed after verifying that the temperature gradient is still negative following the second wait period and/or after comparing the outlet temperature to the one or more outlet temperature setpoints (e.g., determining whether the outlet temperature is less than both the upper outlet setpoint and the lower outlet setpoint, as described above). In embodiments which include the third wait period, the method  200  may also include a third slope check, e.g., verifying that the temperature gradient is still negative after the third wait period. 
     As illustrated at step  214  in  FIG.  3   , in some embodiments, the method  200  may include storing a present value of the monitored temperature, e.g., in a memory of the controller, after verifying that the temperature gradient is still negative. In various example embodiments, the present value may be stored after verifying that the temperature gradient is still negative following the second wait period and/or after verifying that the temperature gradient is still negative following the third wait period. 
     Still with reference to  FIG.  3   , in some embodiments, the method  200  may include a step  216  of comparing a difference between the stored present value and the stored peak value with a predetermined threshold. For example, the difference between the present value and the peak value may be a mathematical difference determined by subtracting the present value from the peak value. Comparing the difference between the stored present value and the stored peak value with the predetermined threshold may include determining whether the difference between the stored present value and the stored peak value is greater than the predetermined threshold. 
     In at least some embodiments, e.g., as illustrated at step  218  in  FIG.  3   , the method  200  may then include determining or detecting a nuisance trip because the difference between the peak value of the monitored temperature and the present value of the monitored temperature is greater than the predetermined threshold. 
     In at least some embodiments, after detecting the nuisance trip, the primary heat control system temperature setpoints may be lowered in order to reduce the chance of another nuisance trip. For example, with lower primary heat control system setpoints, it is more likely that the heating system will be controlled by or in response to the primary heat control system before reaching a temperature at which the thermostat(s) of the secondary heat control system will trip. In some embodiments, a count may be increased, e.g., by one, after detecting the nuisance trip. In such embodiments, lowering the setpoints of the primary heat control system may be performed after the count reaches a limit value. 
     Turning now to  FIG.  4   , embodiments of the present disclosure may also include the method  300  of detecting a nuisance trip of the secondary heat control system, e.g., one or more thermostats thereof, in a dryer appliance. Method  300  generally comprises looking for the monitored temperature, e.g., the inlet temperature, to increase after the heating system has been on for a minimum time. More specifically, as illustrated at step  302  in  FIG.  4   , method  300  may include monitoring a temperature within the dryer appliance, such as an inlet temperature within a supply duct thereof or otherwise upstream of a chamber thereof, with a thermistor of a primary heat control system of the dryer appliance. 
     The method  300  may then include determining that at least one relay configured for providing electrical power to the heating system is on. For example, as illustrated at step  304  in  FIG.  4   , the method  300  may include checking the relay signal, e.g., determining a relay signal is calling to close a relay and thereby activate a heating system of the dryer appliance. Also as illustrated in the exemplary embodiment of  FIG.  4   , the method  300  may include a step  306  of verifying that the relay turned on, e.g., that the relay is closed, when there is a signal to the relay calling for such. 
     After verifying that the relay is closed, the method  300  may include a step  308  of allowing a minimum on time to elapse. In various embodiments, the minimum on time may be between about five seconds and about ten seconds, such as about seven and a half seconds. 
     In some embodiments, e.g., as illustrated at step  310  in  FIG.  4   , the method  300  may also include determining a temperature gradient of the monitored temperature based on a rate of change in the monitored temperature over time. For example, the temperature gradient may be a slope of the temperature over time. A positive temperature gradient may correspond to increasing temperature, whereas a negative temperature gradient may correspond to decreasing temperature. 
     The method  300  may then include determining whether the temperature gradient is negative, e.g., as illustrated at step  312  in  FIG.  4   . When the temperature gradient is negative after the minimum relay on time has elapsed, a nuisance trip may be detected. For example, the method  300  may include a step  314  of detecting a nuisance trip because the determined temperature gradient is negative after the minimum relay on time. 
     Embodiments of the present disclosure include dryer appliances and related methods with indirect detection of the status of the thermostat(s) in the secondary heat control system. For example, the dryer appliances and methods disclosed herein may detect a nuisance trip of the thermostat without a direct physical connection to the thermostat. As another example, the dryer appliances and methods disclosed herein may also be useful for detecting a malfunction or fault in the heating system. 
     This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they include structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.