How To Troubleshoot A Furnace Constantly Running

Posted on: 4 April 2018


Your furnace brings you comfort when you need it, so you hope it keeps working properly. However, you may find the furnace not turning off, which sends you into a panic.

Most furnaces are set to turn off when they reach a certain temperature, but they can fail for many reasons. Luckily, you should be able to troubleshoot the issue yourself by following these tips before calling a heating repair technician.

Adjust the Thermostat Setting

Sometimes, another person may set the thermostat higher, which places strain on the unit, so it keeps running  Compare the room temperature to the preset temperature on the thermometer. Lower the thermostat four or five degrees lower than room temperature, and wait about five minutes to allow it time to shut off the heat.

The furnace may not shut off, if you have set an unreasonable temperature. For example, if the room temperature shows 70 degrees  and you set the thermostat at 90 degrees, it has to work harder to keep up with the setting,  

During cool weather, move the thermostat to the lower setting, ensuring the room temperature is over that setting.  Do the opposite in the summer setting the thermostat to the highest setting, making certain the room temperature is lower. 

Also, make certain the unit is set to "AUTO", and the unit is turned to  "HEAT or "COOL" as needed. Furnaces set to "ON' will keep the blower motor running. If the unit still runs, there is another issue.

Check Thermostat Wiring and Unit Controls

Check to see if the reset button on the furnace has popped, and push it back in place. Turn off the furnace, and inspect the unit for other controls stuck in the down position, and use pliers to pull them back in place. 

Remove the thermostat, and examine the wiring for damage and incorrect wiring. Refer to your manual for the correct wiring of the thermostat, and compare the thermostat wiring to it. Most thermostats have red and white wires. If wires are damaged, replace the thermostat.

Test the limit switch continuity with a voltmeter, and replace malfunctioned switches, or get it replaced professionally. The furnace limit switch is commonly found under a silver or white cover on top of the main heating duct, and it tells the furnace when to operate.

Clean Filters

The furnace filters collect debris and dust to keep them out of the electrical components. Dirty or damaged filters cause the unit to run constantly, since it restricts air flow.

Furnace filters are commonly located near the intake-outtake blower, and they should be removable by hand. Soak removable filters in soap and water, and let them dry, and wipe non-removable filters with a damp rag. Clean filters three months to keep air flowing, and replace damaged filters.