Common Furnace Problems and Their Solutions

Having a furnace is a great boon for any household but it also requires a lot of effort and maintenance to keep the furnace in good working condition. This means that you’ll need to perform regular seasonal maintenance, clean the furnace’s filters, protect it from wear and tear, make sure the thermostat is always working well, and more.

Furthermore, you’ll also need to know how to identify some of the common furnace problems that may arise – how to tell if furnace ignitor is bad, how to spot ventilation problems, and so on. To help you out with that, below we’ve compiled a list of the main furnace problems and their solutions.

The furnace won’t turn on

If your furnace’s not turning on automatically there are a few troubleshooting steps you’ll need to take to remedy the situation:

  1. Check the circuit breakers. Even if your furnace runs on natural gas or propane, it still needs electricity for some of its functions. If the circuit breaker is off, turn it on. If you suspect an overall problem with the electrical grid or the circuit breaker, call an electrician.
  2. Check the thermostat. Thermostat problems are one of the most common reasons for furnace issues.
  3. Check the condensate pan of the furnace. If it hasn’t drained or pumped its condensation water and is full to the brim, this could be the reason why your furnace isn’t turning on.
  4. Check the air filters. If your furnace’s air filters are clogged the furnace won’t turn on. That’s one of the main reasons why it’s important to regularly check and clean or change your air filters.
  5. Check the blower motor. To do that you’ll need to peek through the plastic window on the side of the furnace – if the light there is blinking in green, the blower motor is operating as it’s supposed to. If it’s turned off or is blinking in another color – call a technician, the problem is in the blower motor.
  6. Check the pilot light. Not all furnaces have a pilot light but if yours do and it’s off – turn it on. Most modern furnaces will not turn on if the pilot light is in order to avoid pumping massive amounts of gas into your home.
  7. Check your gas or propane supply. If you’re out of fuel the furnace can’t start.
  8. Check the ignition sensor. This step is more technical and varies in execution from one furnace model to another. We’d generally recommend contacting a professional if this step is necessary. If you want to do it yourself you’ll need to list through the instructions manual or call the furnace’s manufacturer to help you locate the ignition sensor (also called flame sensor). After that, we’d suggest this video guide for how to clean the flame sensor:

The furnace runs then shuts off and starts again

If your furnace is frequently restarting itself, that’s a common problem that’s called “short cycling”. The most common cause of that are problems with the heat exchanger so you’d want to check that first. If that’s not the problem, take a look at the thermostat as it may be faulty.

After that, check the filters and the vents as restricted airflow is another common cause for short cycling. Flame rod failure is also common that’s fixed by cleaning the flame rod so that it can better sense the burner flame.
If neither of those is the problem you can go through the rest of the steps we’ve listed above just to be sure that everything is in order. If you still don’t find the problem, call a professional.

The furnace pilot light won’t stay lit

There are several main reasons why the pilot light won’t stay lit on furnaces:

  1. Faulty thermocouple flame/ignition sensor. Check out the instructions above to see what to do in that situation.
  2. The pilot orifice is dirty. To fix that you’ll need to disassemble the pilot and clean it of debris with a needle or compressed air. This is something that should be done as part of your furnace’s seasonal maintenance.
  3. Faulty gas regulator. If that’s the problem then the rest of your gas/propane appliances should also be affected. You should call your utility company immediately.
  4. Natural gas or propane availability fluctuates. Again, this should affect your other gas appliances – contact your supplier as soon as possible.
  5. There’s too much airflow or draft and it’s blowing the pilot light off. This can happen on extremely windy days or it can be caused by a leak in the output duct of the furnace. To avoid that you should regularly clean and maintain all intake air registers in your home.

The furnace doesn’t stop

If your furnace keeps running after temp reached this means that the furnace burners aren’t turning off. The most common cause for that are issues with the thermostat so check that first.

It can also mean that the air filters are too dirty and prevent the furnace from heating your home, hence why it keeps running. Clean the air filters to fix this problem.

A third possible problem is that the pilot light might be out. Go to the previous section to fix this problem.

The furnace not blowing air through vents

The most likely causes of this problem are:

  1. Thermostat issues.
  2. Clogged air filters.
  3. Circuit breaker problems.
  4. Blower fan issues.

If you’ve checked all of those and you still can’t find the problem, we’d recommend contacting a professional for help.

The furnace won’t reach the set temperature

A typical problem here is insufficient airflow. To fix that you should make sure that there are no problems with the system’s ducts, vents, and air filters.

Another cause for the problem can be a faulty thermostat. If that’s not the case either, check if the flame/ignition sensor needs cleaning.

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