Understanding the Causes of Delayed Furnace Ignition


Does your furnace make a loud booming noise similar to a small explosion whenever it turns on? This booming noise indicates that there is some issue that is causing a slight delay before the furnace ignites. An ignition delay causes gas to fill the combustion chamber before the furnace ignites, producing a fireball or small explosion once the gas finally ignites. Keep reading for a closer look at what issues can cause an ignition delay and also what risks delayed ignition poses.

The Risk of Delayed Ignition

Delayed ignition is a fairly serious problem that has the potential to do major damage to your furnace. In many cases, the heat and vibration from the explosion can crack the furnace’s heat exchanger, which can be extremely dangerous as it can allow carbon monoxide to escape into the home. Should the heat exchanger crack, you will most likely need to replace your furnace unless it is still under warranty. The heat exchanger can be replaced, but it is a costly fix and will often cost about the same as replacing the entire furnace. Now that you know why delayed ignition is such an important issue. Let’s look at some things that can cause it to happen.

Dust and Debris

The most common reason a furnace will experience an ignition delay is dust and debris coating the furnace burners. If the burners are dirty and coated with dust, it can result in the gas ports becoming clogged. When the furnace ignites, the burners usually light in sequence, with one burner lighting the next. If the gas ports are clogged, it prevents the burners further down the line from igniting immediately. This then allows too much gas to flow into the combustion chamber and causes an explosion once all the burners finally light.

This is one of the easiest furnace issues to avoid, as all it takes is having the unit professionally maintained every fall. During this maintenance call, one of our technicians will fully inspect the furnace and clean the burners, flame sensor, and all the other components.

Unfortunately, this problem poquires much more than simply cleaning the burners. The burners can be cleaned to remove the rust and allow gas to flow out of the ports properly. However, if the corrosion is too severe, you will most likely need to replace the burners. Still, this is far better than replacing the entire furnace due to a cracked heat exchanger or another more serious issue.

Sulfur Residue

Sulfur is a natural by-product produced whenever natural gas or propane is burned. Although most of the sulfur is vented through the exhaust flue, some white sulfur residue will always be left inside the combustion chamber. This residue can eventually accumulate to the point that it begins to block the gas ports leading to a delay in ignition. Again, this issue can easily be avoided by having your furnace cleaned yearly.

Malfunctioning Electronic Igniter

Unless your furnace was installed before 2010, it likely uses some form of electronic igniter instead of the traditional standing pilot light found in older units. Any furnace with an electronic igniter will have a built-in safety mechanism that will automatically close the gas valve within a few seconds if the electronic igniter fails to light the furnace for any reason. Unfortunately, however, this safety mechanism doesn’t always activate instantly.

If the igniter is malfunctioning and doesn’t light the gas on the first attempt, it will continue to attempt to light until the safety mechanism activates and shuts off the gas flow. Unfortunately, this means that gas will still flow into the chamber for a short time and lead to an explosion should the igniter finally work correctly. This problem is fairly rare, but it can still occur, and the only solution is to have the electronic igniter replaced.

If your furnace is having issues with delayed ignition, Texas Air Authorities, Inc. is here to help you overcome them. We service and repair all brands and types of furnaces, and we can help if you need to replace your furnace. We also install, service, and repair air conditioners, heat pumps, ductless mini splits, ductwork, exhaust fans, smart thermostats, and a wide range of indoor air quality equipment. If you need a furnace inspection or any other residential or commercial HVAC service in the Arlington area, give the expert team at Texas Air Authorities, Inc. a call today.

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