Common Furnace Problems

When it seems like something’s wrong with the furnace, you can’t help but think about how great it was when everything was working properly and your home was nice and toasty. If you’re looking for some answers to the common issues that might be affecting your heating system, read on!

Why is the furnace running, but there’s no heat?

The first step to solving any problem is to check the simple things first. One of those simple things is your thermostat. If you have a digital thermostat, it’s easy to do: look at the display and make sure your furnace is on and set to heating.

Check your filter. If your filter has become clogged, it can cause your furnace to overheat and turn off. If this happens, your system will continue to blow air into your home, but will get progressively colder.

If you have a gas furnace, check your gas source. It is common for propane tanks to run empty without the homeowner realizing it. Or perhaps your city gas meter has been turned off for one reason or another. Either of these could result in your furnace running without heat.

The furnace takes a long time to turn on

Electric furnaces need a significant amount of electricity to run. The wiring to your furnace is probably fine, but the electrical panel may be overloaded. If your electric heat has tried to turn on, it could have tripped a breaker or blown a fuse. If one of the breakers feeding your unit has been shut off (it is common for them to contain two separate breakers), it will likely take a long time to warm the air in your home. Try temporarily turning off some of your other appliances, or call an electrician to check for any circuit breaker issues.

The thermostat is set incorrectly, or the old thermostat needs replacing. Check your thermostat settings to ensure it’s set correctly. Then check whether it’s an old model that may need to be replaced with a newer model. New models tend to have more precise controls and better sensors.

A dirty filter may be causing the unit to get too hot and shut off. This can cause the unit to quit working altogether or possibly cause your furnace to run for shorter periods of time. Your home may start to get warm, but then it will begin blowing cooler air.

If the furnace turns on and off frequently

If your furnace is turning off and on, then the first thing you will need to check is your filter. But, it is not always the filter that is at fault. You may have a dirty flame rod. This is the sensor that tells your unit it is heating up properly. It could also be a gas pressure problem or a weak or rusty exhaust fan. If the exhaust gasses are not being pushed out of your home quickly enough, it will cause your unit to turn off for safety.

The furnace makes strange noises

Strange noises can be a warning sign that there is a problem with your furnace. If you hear any of the following sounds, it’s time to call a technician.

  • A clicking or buzzing noise could mean a short in the blower motor, which may require a replacement. It could also be your heat strips causing the buzzing sound while they warm up.
  • A humming noise may indicate an issue with the capacitor or electronic circuit board. This may require replacement parts and labor to fix it properly.
  • A banging or clunking sound could be caused by loose belts in your system – a common issue on older furnaces that must be tightened before functioning correctly. It could also be your ductwork being pressurized or depressurized.

Ignition cycle failure

The ignition cycle is the cycle your furnace goes through to begin heating your home.

For modern gas furnaces, you will first have your exhaust fan come on. This is easy to hear from outside the unit. The exhaust fan will have to close a part called a pressure switch to ensure that it can exhaust the gasses from your home. Next, your ignition source will begin working. This may be a hot surface igniter that will glow red or a spark igniter that will start making a clicking noise when it is sparking. Then a click will signify that your gas valve is opening, after which you will hear a jet-engine-type noise as the burners light, and finally, your flame sensor will tell your unit that it has flames.

If you can observe your gas furnace while it is trying to light up, you can tell which stage of the ignition cycle is not working. This may allow you to fix it yourself if it is a simple part, or you can let your HVAC technician know what has gone wrong.

Furnaces can be tricky, but there are some common issues you can look for

Furnaces are usually pretty reliable, but they can still experience problems. Even if the furnace is in good condition, it may need to be serviced or replaced. But before you call a repairman for help, try some of these tips first:

  • Check the thermostat for correct temperature settings.
  • Make sure all air vents are open and clear of debris.
  • Confirm that nothing is blocking the air filter by checking it with a flashlight and a vacuum cleaner attachment.

If none of these steps work to fix your problem, contact an HVAC professional who can diagnose and fix your heating unit.


When your furnace isn’t working as it should, it can cause much discomfort, but don’t worry! The good news is that we listed plenty of common problems you can quickly troubleshoot and fix without calling a professional. If you have any questions about your furnace, contact Honest Air today!

Experiencing any of these problems or have other questions?

Call us today at 301-943-0833