7 Most Common Gas Furnace Problems

What’s wrong with my gas furnace? Why isn’t my furnace working? Can I fix my furnace on my own? Do I need to call a furnace repair person?


Every winter, we hear questions like this from our customers, and to help you out, we’ve put together a short guide of the most common gas furnace issues as well as a few troubleshooting tips and guidance on when you need to call in the pros.

1. Doesn’t Start

If your furnace doesn’t cycle on, try these steps:

  1. Look for a switch located near your gas furnace and make sure it’s turned on.

  2. Check the circuit breaker to see if it has tripped, and reset if needed.

  3. Make sure the thermostat is set to “heat” rather than “cool” or “off”.

  4. If the thermostat doesn’t have a display, replace its batteries or make sure that its wires are attached properly.

  5. Change the filter. Some newer gas furnaces are designed to shut down automatically if the filter is excessively clogged. Simply clean or change the filter to address this issue.

If you’ve worked through these steps and your gas furnace still doesn’t turn on, call an AC repair person — your furnace’s main circuit board may be bad, the draft motor may not be working, or you may have another problem.

2. Blowing Cold Air

In some cases, your gas furnace may blow cold air because it’s not getting any power. To check, turn the fan to “on” on your thermostat. If the fan doesn’t come on, you should work through the power troubleshooting steps above.

If the fan works, your system is getting power and the cold air may be related to the following:

  • Gas not flowing into the system

  • Broken gas control valve

  • Failing ignitor

  • Malfunctioning draft motor

  • Blocked fresh-air intake

You can manually remove snow or debris blocking your fresh-air intake, but you need an AC professional for the other issues.

3. Draft Motor Running, But Furnace Not Starting

Also called an inducer motor, the draft motor pulls combustion gases through the furnace to be released out of the exhaust stack. If you can hear the motor but the furnace never starts, try to locate and clear your fresh-air intake and exhaust chimney. If that doesn’t work, you need to contact a professional because the culprit may be the control panel, gas valve, or ignitor.

4. Constantly Running Blower

To stop the blower from running, make sure the fan switch on the thermostat is on “auto” — the “on” position makes the blower run constantly. If “auto” is already selected, the constantly blowing motor may be due to an issue in the control board or a broken thermostat.

5. Short Cycling

Short cycling is when your furnace turns on and off excessively. In some cases, just replacing a dirty filter or buying a new thermostat can fix the issue, but you may need a new flame sensor or another professional repair. Short cycling also happens when your equipment is too powerful for the amount of space you’re trying to heat.

6. Cold House

If your gas furnace is running but your home isn’t warm, the issue may be the filter. Make sure you have the correct filter and that it’s clean and installed correctly. Leaky ducts can also cause your home to feel cold, and whistling sounds are one indicator that you need to contact a professional to seal your ductwork.

7. Noisy Furnace

Unusual noises can indicate a range of different problems with your gas furnace, including a dirty filter, worn out bearings in the motor, or leaks in the furnace cabinet. Of course, you can change the filter yourself, but you need to call in the pros for the other issues. Additionally, if you have a single-stage furnace, it may run on high capacity at all times, which can be a lot louder than a multi-stage furnace that adjusts its capacity as needed.

8. Bad Odors

If funky odors are wafting out of your ducts, make sure your filter is clean. Then, check the drip pan for moldy build up. Otherwise, the issue could be a dead rodent somewhere in the furnace or ductwork, and you may want to consider professional duct cleaning.

As you can see, some of the most common gas furnace problems can be avoided just by keeping your filter clean. You can troubleshoot many other common issues on your own, but sometimes, professional help is a necessity.

At N.E.T.R., Inc, our technicians are ready to deal with all gas furnace issues from the biggest to the smallest. Need a repair for your gas furnace? Want to set up a service call to help you avoid unexpected repair issues in the future? Then, contact us today.

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