When the furnace doesn’t turn off, you have a frustrating and worrisome problem. Fortunately, the problem isn’t always severe and doesn’t mean you should call in certified HVAC technicians.
We all like the warmth the furnace can provide in a house in the cold months. When the furnace keeps on operating, its warmth can become uncomfortable and the energy bills are expected to go through the roof. Even if you try, you cannot make your furnace stop operating. You don’t want to open the windows and doors to reduce the temperatures inside and you cannot have the furnace run all the time. A furnace that doesn’t turn off can be just as bad as one that doesn’t turn on.
Here are the most common reasons why a furnace won’t turn off:
Page Table of Contents
The thermostat is set to “ON”
One of the problems with the easiest fix for a continuously running furnace is the improper thermostat set-up. The blower will run without stopping when you set the thermostat to “ON.” Even if the heating system is off, the blowers will continue to run and circulate air inside the house.
When you set the blower to “Auto,” the blower will come on automatically, but only if the furnace comes on. It will not operate all the time. If the furnace’s blower runs continuously, here’s what you should do:
- Take a look at the thermostat’s settings
- Turn the thermostat from “On” to “Auto.”
- Set the fan to “Auto.”
You have to modify the thermostat’s settings
When you have a dynamic family with many things happening all the time, someone might knock on the thermostat by accident and change its settings. You must check the thermostat’s settings if your furnace runs without stopping. If it’s set too high, the thermostat will make the furnace run even when the house is heated enough.
It would help if you turned the thermostat back to a pleasant temperature. You can prevent the accident from happening again by taping over the dial or protecting the thermostat. Once the thermostat is set correctly, your furnace should turn off when it reaches the desired temperature.
The air filter is dirty
A dusty air filter is a common cause of the furnace running continuously. The furnace might run without stopping when dust and dirt clog the air filter. It happens as the air movement is lower than usual, so the furnace works harder and longer than usual.
Here’s how you should check out the air filter:
- Open the air filter’s access panel
- Remove the air filter and replace it if you cannot clean it anymore. Air filters need replacing at least once a year. The air quality of your region and the frequency of using the furnace will impact the frequency of replacing the air filters.
The relay is stuck
Let’s say you can reset the furnace to make it operate correctly. If you reset the furnace but don’t get results, an element might be stuck. You should cause a vibration to see if you can shift any stuck components, such as a relay on a circuit board or a mechanical switch. Here’s how you can do it:
- Turn the furnace on
- Place your palms on the furnace and give it a jolt with your hands. See if the blower stops afterward.
- If jolting the furnace made the furnace stop, maybe one of its components was stuck. However, this means that it will get stuck again and giving the furnace a jolt isn’t a permanent solution. Call a certified HVAC technician for further investigation.
The relay needs resetting
The furnace might need resetting to work as expected. After you reset it, the furnace shouldn’t go back to continuous operation. Follow the next steps to reset the furnace:
- Turn the thermostat from “On” to “Auto”
- Carefully turn the furnace off at the plug or switch
- Let the furnace cool for 30 seconds. You need it to come to a complete stop.
- Turn the furnace back on. If everything’s okay, it should reset on its own and not turn itself back on.
- Turn the furnace off for 30 seconds to reset it.
The gas valve is stuck open
What happens if you unplug the furnace or turn it off at the switch and it doesn’t stop operating? Even if the risk for this situation is minimal, it’s not impossible. When the furnace operates, its gas valve is probably stuck open even after you’ve switched everything off. When the valve is mechanically stuck, it will keep burning natural gas even when the furnace is off.
The tips below should help you solve the issue:
- Detect the gas stop; it’s typically close to the furnace
- Turn the gas off
- Call the pros to check out the furnace
- Turn the gas valve off as well
The contacts of the relay are pitted
If none of the previous fixes has given results, a problem with the contacts in the relay could cause the whole situation. If a tiny spark was inside the system, the contacts got pitted and arc welded themselves closed. A malfunction stops the contacts from opening and makes the furnace run without stopping.
This is an electrical problem that is better left to the professionals. Contact an electrician, as he can also check out the system for a short circuit that could cause the problem.
