What Could Cause a Heater to Fluctuate?

Thermostats and Sensors

• Thermostats control the temperature of air and water in your heater system. They use sensors to judge the temperature at different locations -- for a boiler tank, sensors are often at the top and bottom of the tank. If these sensors come loose or malfunction, or if the thermostat starts sending out the wrong signals, the heater can stop and start again suddenly, trying to reach temperatures that do not exist or failing to heat water at the proper times. This can result in heat fluctuations.

Improper Settings

• Heater settings are another common example of fluctuation causes. Examine the thermostat settings on your heater or boiler to see where they are set. If you have the upper limits set too high, the thermostat will struggle to reach them and then go into emergency shut down when it senses that the temperatures are endangering the system. The result can be a fluctuation between too-hot and too-cold water, which is easily fixed through adjustment.

Pressure Fluctuation in Water Heaters

• In some water heaters, especially tankless heaters, pressure fluctuations can result in temperature fluctuations. The water heater needs a certain amount of time to heat the water. If pressure is low, the heater may be able to heat water effectively. If pressure is high because of using multiple faucets or pump changes, then the water may not be able to be heated in time, resulting in a quick change to colder water.

Leaks in the System

• Your heating system may also develop leaks over time. A leak in a heat exchanger can cause, among other problems, an influx of cold air. In plumbing, sometimes cold water valves can malfunction and leak cold water in the hot water of the heater, resulting in fluctuations even when nothing is wrong with the heating mechanism itself.