Heater Thermostats: Understanding Why They May Fail and How to Resolve the Issue

Have you ever wondered why your heater thermostat is not working properly? These devices play a critical role in maintaining the temperature of your home, yet they can sometimes malfunction. In this article, we will explore the common reasons why heater thermostats may not work as expected and provide solutions to resolve the issue.

Common Reasons for Thermostat Failure

There are several reasons why your heater thermostat may not be working properly. Here are some of the most common ones:

Broken Thermostat: Sometimes, the thermostat itself can be broken or defective. It is possible that the thermostat needs to be replaced. Electronic Malfunction: Electronic thermostats can fail due to technical issues. These issues can range from software bugs to hardware malfunctions. Mechanical Thermostat: Mechanical thermostats, such as the round Honeywell thermostat, can often last for a long time because they have fewer electronic components. However, there are exceptions, and they can still fail. Mercury-Dropped State: Some thermostats contain a drop of mercury in a sealed glass bulb. While not common in modern thermostats, if a mercury-switch thermostat has a drop of mercury and it ruptures, it can fail. This has been a concern for the state regulators, leading to safety precautions.

Understanding How a Thermostat Works

To better understand why your thermostat might not be functioning correctly, it is helpful to understand how it works. For practical purposes, let's compare a light switch and a thermostat.

When you want light to enter a room, you simply throw the switch, and the room lights up. However, a thermostat is not the same. A heater thermostat is designed to call for heat when the room temperature drops below the setpoint. This thermostat either opens a gas valve to start the combustion process on a gas heater or warms up resistive coils on baseboard heaters. Once the desired temperature is reached in a house equipped with a gas furnace, the blower will continue to run until the heat exchanger cools off. This controller is known as the fan limit switch.

Your space often will end up warmer than you want, but without the fan running past the setpoint, the heat exchanger could crack, leading to a carbon monoxide discharge. The workaround for getting the space to the temperature you want is to set the thermostat a few degrees cooler than desired so that the thermostat's deadband (usually 3–4 degrees) ends the fan at the desired temperature. For example, if you want 70 degrees, you should set the thermostat at 66 degrees.

Electric baseboard heating has a similar deadband because the warm metal will radiate until cooled off. Therefore, you should set the thermostat a few degrees cooler for this system as well.

Reliability and Best Practices

Understanding how a thermostat works can not only help you save energy but also help you "dial in" the desired temperature for your space. However, it is important to note that the thermostat's performance can be affected by external factors such as open doors and windows. If you leave the doors and windows open in the middle of winter, the thermostat may not be able to overcome that situation, even if the heater is running continuously.

To ensure your heater thermostat is working properly, follow these best practices:

Check the thermostat readings against the actual temperature in your home. Ensure there are no obstructions around the thermostat that could affect its readings. Regularly clean and maintain the thermostat to ensure it functions correctly. Check the wiring connections to ensure they are secure and undamaged. Consider upgrading to a programmable or smart thermostat for better control and energy efficiency.

By understanding how a thermostat works and taking the necessary steps to maintain it, you can avoid many of the common issues that arise with heater thermostats.