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What Can Cause a Furnace to Stop Working?

Brrr! You throw on a sweater, rub your hands for warmth, and reflexively notch up your thermostat. This house is freezing! But instead of that comforting rush of hot air, there’s silence. Something with the furnace has gone wrong. Beyond the frustration, a furnace on the fritz can be hazardous to your home and should be addressed right away.

But what can cause a furnace to stop working? More importantly, how can you implement a DIY furnace fix? Let the HVAC experts at Aire Serv® offer some helpful tips!

What Can Cause a Furnace to Stop Working

A malfunctioning furnace could be the result of any number of things. Before you dial the repairman, look into these possible solutions on how to fix a furnace:

1. The Thermostat

Before trooping downstairs to dismantle the furnace, check to make sure the thermostat itself is not the problem. Modern thermostats can be confusing and difficult to program and may be the source of your heating woes.

Try to troubleshoot the problem by …

  • Making sure the thermostat is set to “Heat” and not “Cool.”
  • Verifying the time and date are correct. If it is preprogrammed to heat the house at a certain time of day, an incorrectly synced thermostat could be the problem.
  • Checking the temperature setting and make sure it is displaying the desired temperature.
  • Manually inputting the temperature to five degrees warmer and see if the furnace turns on.
  • Investigating the wiring and/or batteries. If it is battery operated, consider switching the old one/ones out. If it is wired directly to a power source, trace the wires back to the power source and look to see if there are any noticeable breaks and weaknesses in the wires. If there are, contact a service professional to assist you in rewiring the unit.
  • Reading the thermostat manual! The manufacturer’s specifications and troubleshoots should be indicated in the booklet that came with the thermostat. If the manual has been lost, check online!

2. The Pilot Light Ignition Switch

A defective pilot light ignition switch is a common root cause of a faulty furnace. Take these steps to evaluate and hopefully correct the issue:

  • First Identify the problem.
    Frequent relighting/cycling, overactive blowers, and limited heat from the furnace could all be signs that there may be an issue with the igniter. A common cause of a deficient ignition switch could be wear/an aged igniter, clogged air filters, a broken temperature limiting switch (shuts off the burner if/when the furnace is too hot), or a power surge.
  • If your gas furnace has a pilot light, attempt to reignite the pilot light by:
    • Turn off the furnace gas and power supply and allow the gas to clear.
    • Next, turn the furnace back on and press the ignition button. Most furnaces will have a smaller red button next to it. Press both simultaneously.
    • If the pilot catches, release the ignition button and hold the small button for a minute more.
    • Be sure to follow any furnace manufacturer’s guidelines.

Turn off the furnace and consult a professional immediately if the furnace emits a banging/scraping noise and/or if you detect the heavy odor of natural gas.

If you are unable to reignite the pilot light, call your local Aire Serv to learn about ignition switch repair or replacement.

  • If you do not have traditional a pilot light:
    If you have a modern furnace without a traditional pilot light, your furnace is ignited via an electronic ignition system like an intermittent pilot ignition or hot surface ignition, consult a reputable HVAC service provider to learn about service options for your electronic ignition system.

3. Components & Fixtures

A furnace is composed of numerous additional fixtures that work in tandem. If one or several of these malfunctions, it can make your furnace go kaput. Check these four items for a possible correction:

  • A Clogged Air Filter
    This may be the most common cause for an under-performing furnace. Check the flat and pleated filters (locate with the owner’s manual) and change if they are filled with dust and dirt.
  • The Circuit Breaker
    The furnace may have been turned off from a power surge. Check the circuit breaker and make sure the switch has not been flipped. If so, turn back on and allow the furnace to cycle as normal.
  • The Blower
    Turn your furnace off and set the thermostat to “Fan Only.” If you hear the fan turn on, the blower is not the issue and can be ruled out. If it does not start, the blower motor or the wiring may be faulty. Have an HVAC pro investigate the issue.
  • Pressure Limit Switch
    This device is a safety mechanism to prevent exhaust from accumulating inside the home. The malfunction could be the result of a failed draft inducer motor, improper air intake, clogged drainage, or failure of the switch itself. A service professional can help you to correctly diagnose this problem and replace the switch.

So, What Furnace Fix Do I Need?

A malfunctioning furnace can be a real headache. But with a little know-how and rudimentary detective work, you may be able to make a DIY furnace fix, or at least narrow down the possibilities!

If the problem is beyond your DIY acumen, breathe easy by calling the HVAC specialists at Aire Serv today at (855) 679-0011 or request an appointment online now to get that furnace (or thermostat) up and running!

Relying on a space heater to stay warm while your furnace is on the fritz? Stay safe with these tips from our friends at Mr. Electric®. Like Aire Serv, Mr. Electric is a member of the Neighborly® family of trusted home service brands.