Do It Yourself Home Repair: Common Heater And Cooler Thermostat Problems

Heater and cooler thermostat problems can cause the heating and cooling systems to not reach the proper temperature setting, shut down or improperly cycle.

Heater and cooler thermostat problems can cause a loss of power to the heating and cooling system. They can also cause the system to run abnormal heating and cooling cycles. The most common problems with heater and cooler thermostats vary from thermostat to thermostat. However, whether you have a low-voltage thermostat, line-voltage thermostat or an electronic thermostat, the most common problems are:

Faulty thermostat

Dirt build-up

Improper settings

Voltage loss

Unlevel thermostat

Out of calibration

A faulty thermostat usually means that the sensing element within the thermostat is either not making good contact or there is a total loss of power. This will cause you to lose both your heating and cooling system. Replace the fuse or reset the circuit breaker to see if this corrects the problem. If it is an electronic thermostat, replace the batteries in the thermostat, too. If the problem still persists, then replace the faulty thermostat, which should correct the problem.

Dirt build-up within the thermostat can also cause a total loss of power to the heating and cooling system. Turn the heating and cooling system off completely and remove the thermostat cover. Clean the thermostat using a clean, soft brush that will remove any dirt build-up. Most of the dirt will build up around the bimetal coil (anticipator), which is behind the body's base. If the switch contacts also have dirt build-up on them, use a small strip of white bond paper and slide it in between each of the switch contacts until all the dirt has been removed.



An unlevel thermostat will cause the temperature in the heating and cooling system to either exceed the desired temperature setting or never reach it at all. This can cause the heating and cooling system to turn on and off repeatedly and run very short cycles. Using a level with a level indicator, remount the thermostat so that it is level, which should allow the heating and cooling system to run their normal cycles.

When a thermostat is out of calibration or the anticipator (bimetal coil behind the base of the thermostat body) is improperly set this too, will cause the temperature in the heating and cooling system to either exceed the desired temperature or never reach it at all. It will cause the system to run very short cycles and turn on and off repeatedly. Turn the heating and cooling system off completely and remove the thermostat cover and locate the calibration nut beneath the temperature setting dial. Using a calibration wrench, which should have been provided with the manual of the thermostat, rotate the nut clockwise until the mercury rolls to the right of the bulb contacts. Then adjust the anticipator using a pen or fingernail, to the proper specified setting, which can be found in the manual of your heating and or cooling system. If this does not correct the problem, you may have a loss of bulb charge within the capillary tube and the thermostat may need to be replaced.

Because each thermostat varies, always consult the manual for the proper settings based on the operating system running. Always remember to turn the heating and cooling system off completely before attempting to correct any problems within the thermostat. If you follow these simple guidelines set herein, you will know how to troubleshoot and correct the most common heater and cooler thermostat problems.

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