Furnace Won’t Ignite? 7 Possible Causes and Solutions

Furnace Won’t Ignite? 7 Possible Causes and Solutions

Furnace Won't Ignite? 7 Possible Causes and SolutionsOne of the situations that we see on a service call is when the furnace won’t ignite or fire up. It’s a common problem and one that we have fixed many times.

In our close to 70 years in business servicing all kinds of furnaces – failure to ignite properly is a fairly common occurrence. The good news is that there are a few remedies that most homeowners can execute themselves, and then if you need to call the experts, we can help.

In this article, I have put together the top 7 possible causes of ignition failure and I have included some fairly easy DIY solutions that can be attempted by the homeowner.

  • Clogged filter
  • Broken or Damaged Thermostat
  • Dirty Gas Burner
  • Broken ignitor or Pilot Light
  • Broken Flame Sensor
  • Drafts
  • Gas Line Problems

If you are looking for some help with your furnace in Havertown, PA, give us a call at (610) 446-7877, or click on the button below to contact us online!

Clogged Filter

Air Filters Being Clogged Can Be A Big Problem For Your SystemYour furnace requires a clean air filter to operate at peak performance. Your filter should be changed out every 90 days or at least 4 times a year assuming that your furnace is operating year round. A dirty air filter is no friend to your HVAC system.

Over time dust and debris will build up on the filter and inhibit air flow reducing air circulation but also adding stress to the system. Without adequate airflow, the ignitor can fail to fire up, preventing the system from working properly.

How to Fix It

Your furnace has a compartment, usually easily accessible, where you can slide a clean or new air filter into the slot. Some filters are washable. Disposable filters can be purchased from most home box stores.

Broken or Damaged Thermostat

The thermostat is the control center of your furnace. When your thermostat is set to a desired temperature It tells your furnace when and how much heat to produce.

Occasionally, the thermostat can malfunction due to loose connections. If you notice your heater cycling on and off repeatedly it may be due to a faulty thermostat.

How to Fix It

Do the easy tests first. Check for loose connections and if possible check to see if your thermostat is achieving the desired temperatures. If your thermostat is still not operating the way it should, it is time to contact an HVAC technician.

Dirty Gas Burners

Since natural gas and oil are combustible energy sources, dirt and debris will accumulate on the burners of your HVAC system preventing them from burning evenly and at the proper level. This build-up of debris will cause your furnace to work harder and inefficiently and can clog the gas valve. Plus, the flames may not completely burn when burners are clogged with debris. This failure to execute a complete burn can create a higher level of carbon monoxide off-gassing.

How to Fix It

You can clean gas burners in place by blowing compressed air through each of them and wiping the outside with a brush or rag. It also helps to keep household dust to a minimum to keep dirt out of your furnace.

This is something we generally recommend you leave for the professionals.

Broken Ignitor or Pilot Light

A broken ignitor or pilot light is a fairly common occurrence, especially in furnaces at the end of their life cycle of 10-20 years.

Furnace Blower Comes On But Won’t Ignite

Sometimes pilot lights or an ignitor can malfunction because of a build-up of debris. In that case, a DIY repair is possible.

How to Fix It

First attempt to blow compressed air to remove any build-up of debris. If that doesn’t work, it is time to call an HVAC professional for a diagnostic call and possible ignitor replacement.

Broken Flame Sensor

A furnace’s flame sensor determines if it should continue firing off and will shut down if necessary once it detects a faulty flame signal. A broken sensor can’t regulate when to stop producing heat causing your furnace to overwork leading to premature aging.

How to Fix It

A possible DIY remedy is to clean out the air vents. The best advice is to unplug the furnace and call in an HVAC technician.


Most furnaces are equipped with a draft motor that pulls air from the chimney to help fan the pilot flame. If the motor is malfunctioning or there are excessive external drafts coming from the basement or chimney, your pilot light will have difficulty regulating.

How to Fix It

Check your basement areas for strong external drafts and try to plug them up. If that fails to work, contact your HVAC technician to see if the draft motor needs replacing.

Gas Line Problems

Clogged gas lines can occur in the furnace or in the source of the gas. That is why it is important to keep your furnace and filter clean and free of debris.

How to Fix It

After making sure that your filters and furnace are clear of dust and debris, call in your licensed HVAC technician. Safety first!

How to Relight a Furnace Pilot Light

Hold down the reset button and relight the pilot at the same time. To safely do this, you’ll need to use a long-stemmed lighter and hold the end of it very close to the pilot. Once the flame catches, release the reset button. Watch the pilot light on your furnace for a few minutes to ensure it stays lit.

Furnace Won’t Ignite: FAQs

My Oil Burner Won’t Run: What To Check & What To DoMany problems require a professional repair or solution. If you are looking to fix your furnace in Havertown, PA reach out to

Should I clean or replace a furnace ignitor?

An easy clean is possible to DIY using compressed air. Check out videos on YouTube if you need a little instruction to clean it properly yourself.

How do I know if my furnace ignitor is bad?

If your furnace fires up briefly and then cycles off you may need a replacement. Have a professional take a look to give you a recommendation.

How do I get my furnace to kick on?

  • Check your circuit breakers.
  • Check your thermostat settings.
  • Check your pilot light.
  • Check your blower motor.
  • Check the furnace ignition switch.

If all else fails, give us a call at (610) 446-7877, or contact us online. We’ll take a look at your heating situation, and let you know what has to be done to fix the problem.

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