3 Reasons Your Gas Furnace Won't Stay On

There's nothing more frustrating on a cold winter night than getting a brief blast of warm air from your vents, only for the system to quickly shut down before heating your house. Even worse, your vents may continue to blow cold air, leaving you even colder than before. Unfortunately, these symptoms can signify everything from a relatively minor issue to a much more serious one.

Always check your thermostat first and confirm that your setpoint is several degrees higher than your current indoor temperature. If adjusting the thermostat setpoint doesn't solve the issue, your furnace may be suffering from one of these three increasingly serious problems. 

1. Airflow Restrictions

Your furnace includes many safety switches to protect itself, your home, and your family. These switches stop the furnace from operating unsafely, which may result in equipment damage, carbon monoxide leaks, or gas leaks. The high-limit switch is one of the most important safety elements. This switch stops your furnace from overheating, which may cause the heat exchanger to crack.

One common and straightforward cause of overheating is airflow restriction. Without enough air passing over the heat exchanger, the furnace will quickly shut down but leave the blowers running to cool the heat exchanger. Replacing your filter will often solve this problem, but you'll want to contact a professional if your furnace continues to overheat.

2. Flame Rectification Issues

Flame rectification is the process of "proving" successful furnace ignition. Your furnace's control board must confirm that the burners ignite once the furnace starts. When operating normally, there's a steady supply of natural gas through the furnace burners. If one or more burners don't light, that gas can leak into your home. Flame rectification checks for this condition and kills the gas supply if necessary.

If your furnace runs very briefly and immediately shuts down, you may have a problem with flame rectification or ignition. The underlying cause may be anything from a problem with your flame sensor to a faulty igniter, so it's a good idea to have an expert check your system. Remember that flame rectification is an important safety feature, so you want to ensure everything works correctly.

3. Flame Rollout

Flame rollout is one of the most dangerous situations your furnace can face. Under normal circumstances, your furnace's burners should produce flames that burn cleanly into your combustion chamber. If excess combustion gases remain near the combustion chamber, the flames may "hunt" for air by rolling outside the chamber.

This situation can release dangerous carbon monoxide into your home, so all furnaces include flame rollout switches to detect the problem and shut the furnace down. This problem can create lethal hazards, so it's crucial never to ignore a flame rollout code or to attempt to reset your furnace's flame rollout switch. Instead, contact an expert immediately.

Contact a local furnace repair service to learn more.