A dirty or corroded flame sensor can cause your furnace to keep shutting off unexpectedly. The flame sensor detects if the furnace's burner is lit, and if it doesn't register the flame, it will shut off the gas valve to prevent a gas leak.
Dirty Flame Sensor
The high limit switch has a flame sensor rod that detects air temperatures in the plenum of the furnace. If it is dirty, it cannot properly detect temperatures, which is one reason why the furnace high limit switch trips.
For the burners to ignite, they need airflow. The airflow into the furnace comes from the blower fan that draws air through the return air ducts. But if this airflow is choked off because of a clogged furnace filter or faulty blower, the burners may not be able to stay on for long.
A furnace flame sensor can fail due to several reasons, including: Dirt buildup that prevents it from detecting the flame. Corrosion from moisture or improper maintenance. Incorrect positioning within the furnace.
Flame sensors wear over time. However, often the problem is a dirty sensor, rather than a broken one. Since these sensors are designed to have a low tolerance for reading variations, they might misread from the slightest carbon coating.
There is a work-around to waiting. If there is no safety risk (like a gas leak), a furnace can be reset to bypass this wait. Turn off the furnace's power switch and wait 10 seconds before turning it back on.
1. Will a furnace run without a flame sensor? No, a furnace will not operate without a flame sensor.
Flame sensors have an average lifespan of about five years. Therefore, you can expect to need to replace it at least twice before replacing your entire heating system.
Most furnace flame sensors cost less than $20, but if you opt to have a professional HVAC technician make the repair, you can expect to pay between $75 and $250. Need help replacing your flame sensor?
Blocked vents or a clogged air filter may cause your furnace to run and then shut off too early. It's easy to fix these issues on your own. You should change your furnace filter at least once every three months. Follow our guide to do it yourself.
Failed Thermocouple Symptoms
The first is signs of contamination on the tube, which can include discoloration, cracks, or pinholes. Next, check the wiring for any signs of wear or corrosion like missing insulation or bare wire.
Faulty or dirty flame sensor
If the flame sensor gets a layer of grime over it or becomes faulty, it may mistakenly shut off the gas even though the burners ignited. Professionals can clean or replace the flame sensor to correct this.
A furnace cycling on and off repeatedly can be caused by various reasons, from dirty filters and obstructions in ducts and registers to incorrect thermostat settings and faulty limit switches. By following the steps above, you can help prevent your furnace from cycling too frequently and save energy costs.
Having a working flame sensor is critical for a functioning furnace. While most furnaces last for 10 to 20 years, flame sensors have a much shorter lifespan of about five years. Usually, when a flame sensor goes bad, the best route is to replace it outright.
Short cycling is a common sign of a bad flame sensor. The sensor thinks that there isn't a flame, so it shuts off the gas as a safety mechanism.
It is not likely a flame sensor needs to be replaced. You should be able to sufficiently clean a sensor no matter how dirty it is. But they are not expensive parts, and you can choose to replace it instead of cleaning it. There are different shapes of flame sensors so be sure you are purchasing the proper kind.
Similar to a thermocouple, replacing a flame sensor can be a hard task and should usually be left to the pros.
The flame sensor can become corroded due to carbon buildup from the flame. This can cause the sensor to fail. If the burner light goes out within seconds of switching on the unit, this is a telltale sign of a dirty sensor. If you see soot clearly covering the sensor, then it's time for a cleaning.
The flame sensor within a furnace was created to ensure that the gas valve is opening only while the flames are burning. Otherwise, toxic gas could build up and result in a leak or fire. Flame sensors can be found in all modern gas furnaces and other gas-powered heating systems.
FLAME SENSOR VS.
Thermocouples are used on standing pilot furnaces that have pilot lights. The thermocouple sits near the pilot light and gauges whether it's working properly, while the flame sensor detects that the burners are lit once they start to emit gas and the igniters light them up.
There are four common reasons why a furnace would short cycle; It has a dirty air filter inhibiting airflow to your blower motor, your thermostat is malfunctioning, you have poor insulation, or your furnace is oversized.
The flame rollout sensor will only trip if the furnace has an underlying problem, such as blocked vents, overheating, or gas pressure issues. Ensure that you don't opt to keep resetting the switch and keeping the furnace running.