Troubleshooting Common Furnace Problems

When the days get shorter and temperatures get cooler, your furnace plays a major role in keeping your home pleasantly warm. Because furnaces have a longer dormancy period than air conditioners, problems can pop up after months of neglect. Whether you have a gas or electric furnace, here are troubleshooting tips you can use to get to the bottom of common problems.

Pilot light won’t turn on

Older furnace models use a standing pilot light for power, while newer models use electronic ignition. A pilot light ignites the gas, which heats the air in the combustion chamber. If the pilot light fails, the furnace won’t turn on. If your furnace’s pilot light won’t turn on, it’s possible to relight it on your own. However, if you feel unsafe doing so, you can always call a professional.

For safety reasons, it’s recommended that you use either a long fireplace match or an 11-inch gas lighter to re-light the pilot, rather than a standard match or handheld lighter.

  1. Turn your thermostat to a temperature that will demand heat—for example, 80 degrees.
  2. Locate the pilot valve on the furnace. This is a box-shaped device typically located near the gas burners. It will have a knob with options along the lines of ON, PILOT, and OFF.
  3. Turn the knob to the OFF position. Then, wait 3-5 minutes for residual gas to clear.
  4. Turn the knob to PILOT and prepare to light the pilot.
  5. Place the tip of your lighter at the pilot, while simultaneously depressing the knob to maintain gas flow.
  6. Once the pilot stays lit, slowly withdraw your lighter and release the knob. Then, turn the knob from PILOT to ON. This will ignite the burners.

If the burners fail to ignite, repeat the above steps. If you try again and the burners still fail to ignite, or the flame won’t stay lit, you may have a failing thermocouple or a bad gas regulator. Either way, you’ll want to work with an HVAC technician to determine the cause.

Electric furnace ignition issues

Electric furnace systems are more energy-efficient than older standing pilot designs, but they’re not without their problems. If your electric furnace isn’t working, the causes could include:

Old igniter

Ignition systems don’t last forever. If your furnace is a few years old, it may be time for a new igniter. It’s ideal to have a professional replace the igniter. If the new igniter doesn’t match your furnace’s voltage, it will fail.

Overpowered current

Power surges can overwhelm the igniter and cause it to burn out. If your furnace tripped a breaker, locate your home’s circuit breaker box and flip it back to “on”. If the furnace immediately trips the breaker again, call a professional.

Malfunctioning temperature limiting switch

A temperature limiting switch is one of your furnace’s safety features. If the furnace becomes too hot, this switch turns off the burner. If the switch is broken, or if your air filters are clogged, it can cause the igniter to turn off too early. Try replacing your air filters and see if that fixes your issues. If not, the next step is to call in the experts.

Furnace makes noise

Modern furnaces are designed with noise reduction in mind. Aside from startup noises like a brief bump or clank, you shouldn’t notice many loud or annoying sounds coming from your furnace. Any of the following noises should be considered signs of a larger problem.

High-pitched squealing or screeching noises

A high-pitched squeal or constant screech from your furnace isn’t normal by any means. You’ll need to work with a professional to for sure know what the problem is, but squealing noses can result from:

  • Loose or damaged blower belts
  • Moving parts in need of lubricant
  • Broken or malfunctioning blower motors

Scraping noises

Scraping noises are typically caused by a blower wheel that’s come loose and started hitting its casing. The sound is loud and unpleasant, like nails on a chalkboard. It’s important to call a technician as soon as this noise starts, because it can cause significant wear-and-tear on your furnace. It’s also extremely unpleasant, and you’ll likely want it fixed as soon as possible to restore peace and quiet in your home.

Pops and bangs

Most banging and popping noises are nothing to worry about. What you’re probably hearing is your air ducts expanding and contracting. Other common causes include:

  • Clogged air filter
  • Closed vents
  • Poor quality or undersized ducts

Buzzing or humming

If your furnace is buzzing, the transformer box is probably to blame. The transformer takes incoming power and transforms it into the voltage required for the furnace. A loud humming noise indicates that the transformer is starting to go bad and should be replaced immediately.

Thermostat isn’t working

If your thermostat isn’t working right, your furnace won’t work right either. A malfunctioning thermostat can lead to short cycling, no heat, and rooms that never quite feel warm enough. That’s why it’s important to address common thermostat problems before they turn into big (and expensive) headaches.

Power and batteries

If your thermostat isn’t working, make sure it’s on and set to “heat”, not “cool”. Simple as it may seem, you’d be surprised how often professionals are called out to fix a heater when the only problem is that it’s not turned on. Then, check to see if the batteries need replacing. A low battery indicator will display on the thermostat’s screen to let you know when it’s time to replace them, but this can be overlooked.

If you’re unsure of how to replace your thermostat batteries, consult your owner’s manual for instructions specifically tailored to your model. In general, to replace your thermostat batteries in a thermostat that does not have an external battery compartment, you’ll follow these steps:

  • Pull the thermostat box off its wall mounted plate.
  • Turn the box over and use a small screwdriver to open the battery slot.
  • Discard the old batteries and replace them with new ones, then close the battery slot.
  • Put the thermostat box back onto the wall mount and slide it down until you hear it snap or click back in place.

If your thermostat has an external battery compartment, press down on the top right corner of the thermostat to reveal the compartment. Then, remove the compartment to replace the batteries before snapping it back into place.

Thermostat calibration

If your thermostat isn’t reading the temperature of the room completely, it won’t send the right signals to your furnace. This leads to rooms that feel too cold, or too hot, for comfort. The way to fix this is by recalibrating the thermostat. But first, you’ll need to verify that it needs to be recalibrated.

To do this, you’ll need the following:

  • Glass tube thermometer
  • Tape
  • Paper towel

Start by taping the glass tube thermometer to the wall, a few inches away from your thermostat. You don’t want the thermometer to directly touch the wall, so pad it with a paper towel. Turn your thermostat on and wait 15 minutes before comparing temperature readings.

If the difference between what your thermostat says and what the thermometer says is more than a degree, your thermostat may need to be recalibrated. This is usually done as part of annual heater maintenance, but you can have it done at any point in the heating season.

Furnace problems? Trust Chas Roberts

When your furnace isn’t working as it should, trust Chas Roberts to make things right. Our experts will go the extra mile to ensure that your family is safe, comfortable, and warm all winter long. Contact us to experience superior service every step of the way.