3 Quick Fixes When Your Furnace Won't Shut Off
Is your furnace stuck on, continuously blowing out hot or cold air even when it reaches the set temperature? This frustrating issue can make your home uncomfortable and drive up energy bills. Before calling an HVAC technician, there are a few quick DIY fixes you can try to get your furnace to shut off properly again.
Then we'll provide 3 simple troubleshooting tips you can do yourself to try restarting normal operation. With some easy furnace resets and adjustments, you may be able to resolve the problem without a costly service call.
Symptoms That Your Furnace Won't Stop Running
How can you tell if your furnace is failing to shut off appropriately? Here are some of the most common symptoms:
- The furnace continues blowing out warm or cool air even after reaching the set temperature on the thermostat
- The furnace keeps turning on and off repeatedly in quick cycles
- The blower runs continuously without cycling on and off
- Burners stay lit long after the home has been heated to the desired temp
In most cases, this indicates your furnace is stuck in heating mode and needs to be reset to get it to turn off. Let's look at three DIY troubleshooting tips you can try before calling in an HVAC pro.
Fix #1: Check Your Thermostat Settings
The thermostat controls when your furnace turns on and off. If it's not set correctly, it could cause your furnace to get stuck on. Here are two thermostat settings you should check:
Make Sure Thermostat Mode is Set to "Auto"
One easy mistake is leaving your thermostat on "On" rather than "Auto." The "On" setting will force your furnace fan to run continuously regardless of whether heating is needed. This can lead to the fan constantly blowing hot air.
To fix this, simply switch your thermostat over to "Auto" mode. This will allow it to automatically turn the fan and heating on and off as needed to reach and maintain your set temperature.
Adjust Thermostat Temperature Setting
If your heating temperature is set higher than the actual temperature in your home, your furnace will stay on trying to reach the overly high setting. The optimal furnace temperature setting is around 68-72degF when you are home.
Check that your thermostat is not set to heat beyond what's necessary. Lower it to a reasonable temperature for the season. Then the furnace should start cycling off once your home heats to the appropriate level.
Fix #2: Clean or Change the Furnace Air Filter
A dirty, clogged furnace air filter can also cause your furnace to get stuck heating. Here's why:
How a Dirty Filter Prevents Shut Off
As debris builds up on the filter over time, it restricts airflow through your furnace. This forces the system to work harder to keep pushing air through the restricted filter. The increased effort can cause the furnace burners to overheat and fail to shut down.
Replacing a clogged filter removes the airflow restriction allowing the furnace to operate normally again. Aim to change the filter every 1-3 months based on use and your model's recommendations.
DIY Instructions for Replacing Furnace Filter
Replacing your furnace filter is a quick, easy DIY fix you can do in just a few minutes. Follow these steps:
- Locate your furnace filter. It's usually found in a slot near the blower motor or behind a panel you can unlatch.
- Take note of which direction the arrow on the filter is pointing. This indicates the direction of airflow.
- Gently slide out the old dirty filter from the slot.
- Insert the new filter in the same direction as the arrow on the old one.
- Ensure the filter is fully inserted, then close the access panel.
With better airflow restored, your furnace should be able to reach set temps and turn off appropriately again.
Fix #3: Reset Your Furnace
If adjusting the thermostat and cleaning the filter doesn't resolve the issue, try rebooting your furnace for a reset:
Turn Furnace Off and Wait 30 Seconds
Find your furnace power switch, typically located right on the furnace or nearby on the wall. Turn it to the "Off" position. Leave it off for a full 30 seconds before switching it back "On."
This gives time for the furnace control board to fully reset. Restoring full power can clear any glitches causing it to get stuck on.
Reset the Thermostat
You should also reset your thermostat after resetting the furnace itself. Refer to your model's instructions for the reset steps. On smart thermostats, you may need to remove it from the wallplate, wait 10-15 seconds, and snap it back into place.
Resetting both the furnace and thermostat together can help them sync back up properly to restore normal operation.
Check and Test the Furnace Relay Switch
The relay switch helps turn the furnace blower and burners on and off automatically. If it's defective, it could get stuck and lead to continuous heating. After furnace and thermostat resets, check that the relay switch clicks when you turn the thermostat on and off.
If you don't hear it click, the relay may need replacement. Have a technician install a new relay switch certified for your furnace make and model.
When to Call the Pros
If your furnace keeps heating despite these DIY troubleshooting tips, it's time to contact an HVAC professional. A technician can test components like the flame sensor, thermocouple, gas valve and motor. They have the training to diagnose issues and safely perform necessary repairs.
It's also wise to call a pro right away if you suspect a gas leak or a problem with the gas line. Attempting to relight a furnace in that case could be hazardous.
Getting a stuck furnace fixed quickly avoids wasted energy and prevents potential damage from overheating. In the majority of cases, HVAC technicians can get even stubborn furnaces switching off appropriately again.
While a furnace that continues running indefinitely can be perplexing, there are a few easy DIY solutions you can attempt before calling a repair company. Check your thermostat settings, replace the air filter, and reset the furnace and thermostat. In many cases, one of these simple furnace troubleshooting steps should do the trick to halt unwarranted heating.
Pay attention to your furnace and how often it cycles on and off to catch issues early. With proper maintenance and filter changes every few months, you can avoid annoying and costly problems like a furnace that stubbornly refuses to shut off.