What Causes a Thermostat to Go Bad in a Water Heater?

Thermostats manage the temperature changes in hot water heaters. They use input data from sensors placed on the water heater to switch the heater on and off to maintain a certain temperature, often according to settings that the user can change. Most hot water heaters have a thermostat for both the top and the bottom of the water tank to judge changes through the system. Thermostats can malfunction for several reasons, most related to wear and age.

Displaced Sensors

Thermostats can slow down or develop electrical problems.

The sensors that a thermostat uses to sense water temperature can eventually become displaced, falling away from their attachments to the tank. As a result, the sensors do not read the water temperature as high as it really is. This can cause the thermostats to switch on and off due to mismatched readings, or cause the water to reach dangerous levels of heat without the thermostats shutting the system off for safety.


The internal components of the thermostat can eventually wear down and lose efficiency. The thermostat may still work properly, but the method it uses to judge heat, such as a thermocouple, can eventually slow over time. This causes a delay in thermostat reactions, so water may become too hot too quickly or not cool down as easily.

Contaminant Problems

Dust, soot, rust and other contaminants can eventually enter the thermostat and cause problems, especially with its mechanical operation. This can make the thermostat stick so that it fails to send the proper signals to the hot water heater. Thermostats are complex and it is easier to buy a new version than try to clean your old device.

Faulty Wiring

The wires that your thermostat uses to communicate to the sensors and operational systems of the hot water heater also can malfunction. These wires can fray and lose power so they no longer supply electricity to the key areas of the thermostat. A thermostat with faulty wiring dies or does not respond to commands.

About the Author

Tyler Lacoma has worked as a writer and editor for several years after graduating from George Fox University with a degree in business management and writing/literature. He works on business and technology topics for clients such as Obsessable, EBSCO, Drop.io, The TAC Group, Anaxos, Dynamic Page Solutions and others, specializing in ecology, marketing and modern trends.