In this post, we discuss what the causes of your furnace not heating properly might be and what you can do to try and fix it or if you need to call a professional.
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Is your gas furnace is blowing cold air? Is it not heating properly?
When your furnace is not heating properly, there a number of possible reasons.
Some of these you might be able to troubleshoot on your own. Others will require you to call a furnace repair company.
Here is a list of some of the most common problems and possible solutions for getting your furnace working again.
Causes for furnace not heating
- Furnace is off
- Reset needed
- Door cover open
- Filter is dirty
- Pilot light out
- Registers closed
- Flame sensor dirty
The first thing to do is make sure your thermostat is set to “heat”, not to “cool”, and make sure the fan is set to “auto”. As obvious as this sounds, it is a very common problem, so always start there.
After you have made sure it is set to heat, check the thermostat temperature. Make sure it is set to a high enough temperature is high enough that it causes the furnace to turn on and get the heat going.
If the thermostat is set to heat and the temperature is high enough, then check that it is getting power. Check the batteries, the fuses and circuit breakers. Then check that the interior is clean. Heavy dust and debris in the thermostat can cause problems.
These are all easy fixes and could save you from calling a technician.
Even if you’ve checked all these, it’s still possible that you could have a broken thermostat. In this case, you might be able to replace it yourself but often the best option is to call a professional.
Related: Types of Thermostats
Furnace is off
Always check to make your furnace is getting power. Check the fuses and circuit breakers. Make suret the emergency power switch to your furnace has not been accidentally bumped and turned off.
Related: Common Furnace Problems
Most furnaces have a reset button. It is often a red button that you can find on the front, side or back of the furnace. Try pressing the reset button and you just might be lucky enough to get the furnace working again. Just like restarting your computer, sometimes it’s that simple.
Door cover open
If you have recently changed your furnace filter, it’s possible that the door to your furnace has been left open. Some furnaces have a sensor that stops the furnace from turning back on if it is not closed properly.
Filter is dirty
A dirty furnace filter is actually one of the most common causes of your furnace not working. A dirty furnace can stop the air from flowing properly through the furnace and cause overheating. An overheated furnace can stop running because the heat sensors will then stop the furnace so there is not a fire hazard.
If your furnace filter is dirty, change it and press the reset button. Make sure in the future you are changing your furnace filter every 1-3 months according to the directions on your filter. Over time a dirty filter can cause serious problems that could damage the furnace.
Pilot light out
Newer furnaces may not have a standing pilot light, but if you have an older one you will need to check that it is still lit.
Check to see if the pilot light is out. If it is, turn the gas valve to the off position and wait for five minutes. If there is a reset button on your furnace, turn the valve to the pilot position and hold a flame to the dedicated pilot opening while pushing the button for about 30 seconds. When the pilot is lit again, turn the gas valve back to the on position.
If your pilot light will not stay lit, there could be problems with the thermocouple or ignition system. In this case, you will need to call a professional to replace the parts.
Check the register vents around your home. If enough of them are closed at the same time, this can cause heat to build up in your furnace and force air out of duct leaks and requiring the blowers to work harder to make up for the added pressure. It can also force air pressure to build up in your air ducts, which can cause or worsens leaks in joints and seams.
Flame sensor dirty
The flame sensors in your furnace are there as a safeguard against the unsafe burning of fuel. A dirty flame sensor could be causing your furnace to blow hot air properly.
The flame sensor is usually a rod near the back of the furnace, in the direct path of the burner.
To clean the sensor, turn off the power to the furnace from the breaker box. If possible, remove the sensor from the furnace and then gently scrub the sensor to remove any dust and dirt. When it’s clean reattach it and try repowering the furnace again.
We hope that one of these solutions helped get your furnace working again. If you’ve tried everything and it still isn’t blowing hot air, please call a professional HVAC repair person.