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Common Furnace Problems and How to Fix Them

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Common Furnace Problems and How to Fix Them

Fall is upon us and winter isn’t far behind. As temperatures drop and stay low, its vital to our health and comfort that the heat in our home works as it should.

But furnaces need regular maintenance to ensure their durability, longevity and consistent functionality. We hardly notice when they’re doing their job appropriately, but when they don’t… we know it within hours as indoor temperatures begin to plummet. So before you have to break out the blankets and space heaters, have your furnace checked and have any maintenance or repairs it requires performed. 

How do you do that? By scheduling professional heating maintenance every fall. Sign up for a home maintenance plan so this important home maintenance task is always taken care of in a timely manner.

What Could Go Wrong?
Common Furnace Problems and How to Fix Them

If you’re wondering if you really need to call in the professionals, there are a few things you could check first. Sometimes, all that is needed is a filter or battery replacement.

Thermostat Troubleshooting

Often when people think they have a broken furnace, it’s actually a thermostat problem. Here is what to check for on your thermostat:

programmable thermostat

  • POWER – Ensure your thermostat has enough power to send signals to your HVAC system. Check the faceplate for a low battery signal. Remove the faceplate to access and change the batteries if they’re low.
  • DUST – Older electromechanical thermostats may need dusting. So if your thermostat isn’t working, open it up and clean dusty areas with a Q-tip. Ensure you’re going around the bimetal coil and contact plates. If Q-tips can’t fit in the small crevices, a small piece of soft paper should work.
  • LOCATION – Ensure your thermostat is away from direct sunlight and other sources of heat, because if your thermostat is near a heat source, such as a heating vent, light fixture, or cooking equipment, the thermostat will believe the ambient temperature for the whole house matches that of the heat source.
  • BALANCE – For a thermostat to work properly, it should be completely level. This is especially important for older thermostats that use mercury switches. Use a level to check if your thermostat is straight and reposition it if necessary.
  • ADJUST ANTICIPATOR – If you have a non-digital thermostat with a mercury switch, you may need to adjust the anticipator. This means removing the faceplate and locating the small metal tab that goes from shorter to longer. If your furnace is cycling on and off too frequently, try adjusting the anticipator toward the “longer” setting. If the HVAC system isn’t cycling enough, turn the anticipator toward the “shorter” side. Sometimes a little trial and error is needed, so be patient.
  • THERMOSTAT SETTING – This may sound obvious, but make sure your thermostat is set to “heat.” If the furnace still won’t turn on, turn off the furnace at the source and switch the thermostat over to “auto” and wait about 30 minutes. Turn the furnace back on and switch the thermostat back over to “heat” to see if this “reset” did the trick.

If you do have any problems with your thermostat, don’t hesitate to contact us.

The thermostat not the issue? Then it’s time to check the power.


If your furnace isn’t getting power, go to your breaker box and check for blown fuses or tripped breakers. If power at the breaker/fuse box is on, make sure your HVAC system hasn’t been unplugged for any reason. There may also be a separate power switch near the furnace that looks like a light switch. Turn it on.

After ensuring everything is plugged in and switched on, reset power at your breaker box. If restoring the circuit doesn’t work, then you could have faulty wiring between your thermostat and furnace. If this is the case, contact us.

air filter

Dirty Air Filter

If both your thermostat and furnace are getting the power they need, the next thing to check is your furnace filter. Some HVAC systems have a safety device in place to turn off the furnace in the case of a dirty or clogged air filter. It’s important that you replace your HVAC filters every 30-90 days depending on the type of filter you have and how often you use your system. Changing your air filter improves airflow and indoor air quality while lowering heating costs and extending the lifespan of your unit.

Relight Pilot 

If your furnace has power and a clean air filter but still won’t work, there may be a problem with the gas. If you aren’t getting gas or the pilot won’t light, make sure the gas valve is fully open and the pilot light is fully depressed. If you need to relight your pilot, follow the manufacturer’s instructions exactly (hopefully the manual is fastened to the furnace somewhere). If you can’t find the exact instructions, follow these steps:

  • Locate the pilot light assembly and turn the dial to the “off” position.
  • Wait 5-10 minutes until all the gas has dissipated.
  • If you still smell gas after 10 minutes, evacuate the household and call your local gas company and fire department.
  • Look for the ignitor button next to the gas valve with “on,” “off,” and “pilot” settings.
  • Turn the valve over to the pilot setting.
  • Hold a long lighter or match to the pilot opening while you press down on the reset button (usually red).
  • Keep the button depressed until the flame comes on.
  • Switch the setting from “pilot” to “on.”

Bad Pilot Signs

  • Yellow, purple, orange, or red flames
  • Split, flickering, or wavering flame
  • Flames higher than 2 inches or shorter than 1 inch

To adjust pilot light flame height, tighten or loosen the screw located on the pilot valve body. Refer to your manufacturer’s instructions for proper location. Tightening the screw (clockwise) should decrease the flame size while loosening the screw (counter clockwise) should increase it.

If your pilot light won’t stay lit or is any other color than blue, contact us to diagnose the situation. You may have a dangerous combustion situation or a faulty thermocouple (safety device that shuts off the gas).

Sometimes, to fix the thermocouple, all you need to do is tighten the nut with a wrench. Only tighten it a little bit, then try to light the pilot again. If this doesn’t work, the thermocouple may need replacement. And unless you know exactly what you are doing, we recommend calling a pro for the job.

Cleaning, Lubrication, and General Maintenance

Avoid furnace problems with regular maintenance. Schedule a professional tune-up in the fall (or sign up for a home maintenance plan) and replacing your air filters every 30-90 days.

Your technician will lubricate all moving parts, clean the interior and exterior, check for venting and electrical safety, as well as seal leaks and tighten bolts that hold any components in place before test running the heater. If there are signs of bigger issues, he or she will catch it and schedule a repair session. Maintenance helps the heater use less energy in the winter months, reducing your bills as well as running less of a risk of major repairs. These are things you should not attempt to DIY.

When to Call the Professionals

Some malfunctions are obvious—such as a furnace that won’t turn on at all—but others are harder to diagnose, such as changes in the sound the furnace is making. Below are some of the warning sounds that your furnace needs professional assistance you shouldn’t let slip by.

  • Booming: If you gas furnace makes a “booming” sound when it comes on, it usually means there is a defective gas valve or an issue with the burner, such as dirt or rust, that is blocking the gas jets. Cleaning the burner is best left to professionals. 
  • Clicking: A clicking noise as the furnace turns on sometimes indicates problems with the electrical ignition. If the clicking sound occurs after the blower fan turns off, it can point toward cracks in the heat exchangers, which can lead to carbon monoxide leaks in gas furnaces—this can be deadly, so call for repairs immediately.
  • Screeching: This may indicate issues with the blower motor and/or bearings. Have technicians look into the sound and see if the motor needs replacement.
  • Clanging: If you have an older furnace that still uses a blower motor fan belt (rather than a direct motor), clanging noises may indicate the belt has snapped and is starting to strike parts of the cabinet. Although repairs can fix this, in most cases you should give serious consideration to replacing the furnace with a newer model.

Because there can be more than one cause behind a particular furnace noise, a repair technician should be brought in to diagnose and fix the problem. DIY furnace repair can cause more problems that it fixes, including fire, carbon monoxide poisoning, refrigerant leaks, and expensive repairs. If you have any doubts about what you are doing, stop and contact us at Phoenix Air ATX. We’re familiar with all makes and models and can get your heat back in no time.

Peace of Mind for $179 a year

Join our Maintenance Plan Program and get all the perks of membership: 10% discount on repairs, seasonal tune-ups, priority scheduling and more. 100% satisfaction guaranteed.