Why Won't Your Furnace's Burners Ignite?

There are a surprisingly large number of steps required for your furnace to heat your home safely and effectively, but there's no denying that igniting the burners is among the most important. If your burners don't light, your furnace can't provide the heat you need to keep your home warm. Unfortunately, several issues can cause your burners to remain stubbornly cold.

How Do You Know If Your Burners Are Lighting?

There's one obvious symptom of burners that won't ignite: you don't get any warm air from your vents! Of course, depending on the underlying cause of the problem, the symptoms can be slightly more subtle. For example, you may momentarily get warm air from your vents, only for the furnace to shut down quickly.

If you're comfortable with a little do-it-yourself work, you can attempt to check the condition of your flame. Your furnace may have a glass that allows you to see the burners, or you may need to remove the panel. In the latter case, you'll typically need to hold down the door safety switch, or the furnace won't light. Do not tape this switch down and remain at a safe distance while you have the panel off.

Under normal circumstances, you should see the burners quickly light from one side to another. If not, closely watching them can provide insight into what's wrong. Does your furnace remain almost completely silent? Can you hear the draft inducer turn on, but the burners fail to ignite? Do the burners ignite partially or briefly, then turn off? Each scenario provides valuable clues.

What Can Stop Your Burners From Igniting?

If your burners don't ignite, there's likely an issue in your furnace's start-up sequence. For example, you may have a faulty safety switch, or your draft inducer motor may not produce sufficient negative pressure. It's also possible that your gas valve is faulty or providing too little pressure. Whatever the case, your burners are unlikely to be at fault.

On the other hand, partial ignition may indicate a problem with the burners or the gas tube that supplies gas to each one. Your furnace uses a flame sensor at the end of the burners to detect ignition, so each burner must ignite for the flame sensor to give the control board an all-clear. If a blockage prevents full ignition, the control board will shut the furnace down to prevent a leak.

Finally, full ignition followed by a quick shutdown often indicates a flame sensor issue. If the sensor is faulty, it won't allow the furnace to continue supplying gas, even if your burners fully ignite. Unfortunately, it's still necessary to test the sensor since a quick shutdown may also result from a damaged heat exchange or another problem that is causing the furnace to overheat.

Whether you're experiencing partial or no ignition, it's best to rely on an HVAC professional for further diagnosis. Faulty furnaces can potentially be dangerous, so it's best to have an expert locate and repair the problem.

Contact a local heating service to learn more.