How to Know If a Furnace’s Thermostat is Bad

Many homeowners will replace or repair their furnace thermostats as a DIY project, but it is a complex fix for those unfamiliar with the process.

Problems with a furnace can happen suddenly without warning, such as when the furnace won’t operate. Other times, it may be more gradual. It may take forever to warm up the living space, or the furnace may run long after the home is heated, making the occupants uncomfortable and increasing home heating costs. Whatever the circumstance, the likely culprit might be a faulty thermostat.

Those little gauges and dials, whether analog or digital, mounted on a wall control so much. Frequent temperature adjustment does a lot more than cause the occasional family feud. Changing the thermostat temperature setting can reduce the system’s reliability.

If the furnace is under- or over-heating a home, it may not be time to replace it. There’s a very good chance a furnace has momentarily become unreliable due to a problem with the thermostat. The good news is that a thermostat issue is reasonably easy to remedy. 

Here’s how to know if a furnace thermostat is bad.

• Check the thermostat switches to make sure they aren’t loose or broken. Many older thermostats, especially the mercury and analog models, have plastic parts that can snap off or break. If there’s any play or give-in temperature adjustment switch, a new thermostat is the best solution to guarantee the furnace’s efficiency and reliability.

• Remove the furnace thermostat cover to inspect the interior. If there is a lot of dust or grease build-up on the inside, use a can of compressed air to remove the debris. A small paintbrush is effective at removing dust from the tighter spots.

• Look closely to see any loose wires or broken components in the thermostat. If there are, the thermostat needs replacing.

• Use a battery tester to determine if the battery is still good. The thermostat may just need a new one. Check the owner’s manual for guidance.

Once the homeowner has done the above tasks, they should turn the furnace back on and see if it’s working correctly. If the furnace doesn’t engage, shuts off suddenly, or runs without regular interruption, it would be best to replace the thermostat.

Furnace Repair

Many homeowners will replace or repair their furnace thermostats as a DIY project, but it is a complex fix for those unfamiliar with the process. For those who feel a little unnerved dealing with electrical components of their home’s heating and cooling system or aren’t certain the problem is with the furnace thermostat, contacting a reliable local HVAC technician is the best option.