Why Won't My Gas Furnace Stay Lit?

With cooler temperatures coming, many Arizonans are turning on their gas furnaces for the first time this year—only to discover that they won’t stay on! They ask themselves, “Why won't my gas furnace stay lit?”

In this blog, we’ll discuss the following so that you better understand how gas furnaces and pilot lights work and why yours won’t stay lit:

Gas furnaces and pilot lights are pretty complex, so they often require a lot of experience to diagnose and repair. Before we dive into the causes, we recommend reaching out to a technician as the easiest and safest way to get your heating system working.

If your pilot light goes out without lighting the burner or if it never ignites, the issue could be:

Malfunctioning flame sensors cannot detect that the pilot light is lit. For safety reasons, the gas valve will close, and the fire will go out if the flame sensor cannot feel the pilot light. Flame sensors need regular maintenance, cleaning, and occasional replacement.

On many furnaces, the flame sensor is actively touching or is very close to the pilot light. If it’s out of position, it assumes the pilot light isn’t lit and shuts off the gas. In some cases, you might be able to reposition the flame sensor, though it may require replacing.

The ignition board is the component that controls the gas valve, electric spark, and flame sensor. When it fails, the whole system fails. Diagnosing issues with the ignition board can be extremely difficult without professional training.

Sometimes the issue isn’t with the heating system but the gas delivery. A pilot light requires a small but constant gas stream to stay lit. If gas pressure drops due to a leak or other issue, the pilot light can’t burn. You may be able to fix this by replacing the gas valve, but there could be issues elsewhere in the gas line.

When the issue isn’t the pilot light, the burners may ignite and even run for a short period before going out. You might notice that the fan continues to run even after the pilot light goes out.

As a safety precaution, furnaces have limit switches that prevent the burners from burning too hot and causing major problems. Dirty filters, vent blockages, and other airflow issues can all cause the furnace to overheat, triggering the limit switch.

Occasionally, the limit switch simply breaks and requires replacing. It pushes a false positive that the furnace is overheating, so the burners shut off.

The problem with your furnace may lie in the thermostat. For example, regardless of what you set your thermostat to, it keeps telling the furnace that the house is warm enough and there is no need for more heat.

To prevent issues and ensure your furnace keeps working, contact a professional whenever your gas furnace doesn’t stay lit. Some causes of the problem are significant and require immediate professional care.

Hearing hissing or crackling sounds from your furnace can indicate a gas leak or electrical issue. Smells can also signify something serious. For example, rotten eggs mean leaking gas or a burning smell for electrical issues or fire.

If you have identified one of the above issues, you likely want a professional with fast, convenient scheduling. Book with George Brazil HVAC for a same-day gas furnace repair. Our certified professional technicians repair all makes and models.

Phoenix homeowners trust us to treat them with integrity because we value high-quality customer service. Over two thousand 5-star reviews, a 100% satisfaction guarantee, and a Better Business Bureau Torch Award for Ethics back up our work.

Start by calling us at (602) 842-0009 or booking below for a free diagnostic.