While gas furnaces are one of the best options for heating Michigan homes, they can also be prone to developing certain issues that prevent them from working properly. One problem you may encounter is the burner flame going out almost immediately after igniting or the furnace turning off partway through the cycle. This issue is often related to one of the sensors or safety switches, but it can also indicate a much more serious problem that potentially poses a significant health and safety hazard.
Worn-Out or Dirty Flame Sensor
If the burners go out within a few seconds of igniting, you can almost be certain that the problem lies with the flame sensor. The flame sensor is a crucial safety mechanism that ensures the gas immediately stops flowing to the burners if they fail to ignite or the flame goes out. If the gas didn’t shut off, it could easily result in a fire or major explosion.
The flame sensor works by sending out a small electrical current that interacts with the flame, allowing the sensor to confirm that the burners are lit. It continually sends a signal to the control board indicating proper operation. If the flame sensor fails to sense the flame and doesn’t send a signal to the control board, the board will automatically close the gas valve, causing the gas to stop flowing.
The sensor is constantly exposed to extreme heat whenever the furnace is on, which eventually causes it to wear out and stop detecting flames properly. The solution in this situation is to have a technician replace the sensor, which is an easy and relatively inexpensive fix. Dust and soot coating the sensor can also prevent it from sensing the flame. This issue is common if you neglect furnace maintenance, but you can easily prevent it by scheduling annual fall furnace tune-ups.
Malfunctioning Limit Switch
The limit switch is another important safety mechanism that continually senses the temperature inside the furnace to ensure it doesn’t overheat. If it detects that either the heat exchanger or the blower is getting too hot, it signals the furnace to shut off. This switch also signals the blower to turn on once the heat exchanger is sufficiently hot. After the furnace shuts off, it will signal the blower to turn off once the exchanger has cooled.
A faulty or malfunctioning limit switch can fail to sense the correct temperature and shut the furnace down when there’s no danger of overheating. It may also stop working intermittently and cause unexpected shutdowns. Luckily, replacing the limit switch usually won’t cost more than a few hundred dollars. During an annual furnace tune-up, a technician will test the limit switch and can often determine if it’s starting to wear out or malfunction. If issues are found, the switch can be replaced to prevent problems during the winter.
Overheating
It’s also possible that your furnace won’t stay lit because the furnace or blower keeps overheating. Overheating most commonly occurs when the air filter is dirty and clogged, restricting airflow into the furnace. Without enough air flowing across the heat exchanger, it can overheat quickly and trigger the limit switch to shut the system off. A malfunctioning or worn blower can also prevent sufficient airflow.
The first thing you should do if your furnace keeps shutting off midway through a heating cycle is check the filter and replace it if it looks dirty or dark. If overheating was caused by a clogged filter, the furnace should operate normally once the filter is replaced. If replacing the filter doesn’t solve the issue, you’ll need to schedule a professional inspection.
Faulty Pressure Switch
All modern furnaces have a draft inducer that actively draws hot exhaust fumes through the heat exchanger throughout each heating cycle. The draft inducer starts first and typically runs for 15 to 30 seconds before the gas flows and the burners ignite. As it runs, the inducer creates negative pressure inside the furnace, activating the pressure switch. Once activated, the pressure switch signals the control board to open the gas valve.
The switch has a small rubber hose connected to it that allows it to sense air pressure inside the furnace and confirm the inducer is working properly. If the hose is loose or damaged, the switch may deactivate and prevent the furnace from operating. If the hose is disconnected or the switch itself is faulty, the inducer will still run, but the furnace won’t ignite.
Faulty Control Board or Electrical Issue
The control board functions as the furnace’s brain, continually communicating with the thermostat and all safety switches and sensors. If the board is faulty, it may cause the furnace to shut off intermittently because it fails to receive signals from one of the components. It can also stop working altogether. Another possibility is an issue with the wiring connecting a sensor or switch to the control board, preventing proper communication.
A major electrical problem could also cause a wire to short-circuit and trip the furnace’s circuit breaker. If the blower motor is wearing out, it may draw more power than normal, causing the breaker to trip. If your furnace keeps tripping the breaker, it’s essential to have it inspected immediately, as electrical issues can cause significant damage or lead to an electrical fire.
Cracked or Clogged Heat Exchanger
The most serious concern when a furnace won’t stay lit is a cracked or clogged heat exchanger. This is a major safety issue, as it allows carbon monoxide to escape and mix with the heated air. In some cases, air escaping through a crack can extinguish the burner flames. More commonly, exhaust fumes build up in the combustion chamber, starving the flames of oxygen. This causes the flames to grow larger and trip the flame rollout sensor, shutting the furnace off immediately.
Replacing a damaged heat exchanger can be expensive and may cost nearly as much as replacing the furnace. Whether replacement is worthwhile depends largely on the furnace’s age and whether the repair is covered under warranty.
If you’re experiencing problems with a furnace in Farmington Hills or the surrounding areas, you can count on our experts at AJ Danboise Plumbing, Heating, Cooling & Electrical for prompt, professional service. We’re proud to be the area’s top choice for furnace repair and furnace installation. To schedule a furnace inspection or any other HVAC service, contact us today.
