How to Test the Thermostat on Your Gas Furnace for Problems

If your gas furnace won’t start up, the first place to look for the source of the problem is your thermostat. Most thermostats will give you many years of reliable service, but even the highest quality models eventually wear out.

Some thermostat problems are easy to troubleshoot and inexpensive to repair. Before you call your HVAC technician for help, try some of the following troubleshooting tips:

Check the batteries. Most programmable thermostats are battery-operated, so the first thing to do if your gas furnace will not come on is to change the batteries. If you have an older manual mercury-switch thermostat, it may be hardwired into your heating system without any batteries.

Check the thermostat setting. Be sure your thermostat is set to “heat” before you try to get your furnace to come on. Set your thermostat temperature at least five degrees above room temperature, so your thermostat can call for heat from the furnace. You can override your thermostat’s programmed settings by using the “up” and “down” arrows and the “hold” button to change the set temperature.

Check the thermostat programming. If setting the temperature manually makes your furnace come on, but your system doesn’t turn on and off according to your programming, check to be sure the program has not been reset to its default mode due to a power outage. If you can’t find your owner’s manual, you can probably search online by model number to find an online version of the manual.

Bypass the thermostat. If you’re comfortable working with electrical devices, you can remove the wiring from the back of your thermostat and close the circuit by twisting the hot and ground wires together. Do not attempt to do this if you don’t know what you’re doing. Call your HVAC pro, instead. If your furnace comes on when you do this, it’s a good indication that your thermostat has failed and should be replaced.

Call NisAir Air Conditioning and Heating if you’re having problems with your gas furnace or thermostat in your Palm Beach home.