If it's broken or malfunctioning, it may fail to detect the flame and shut off the gas supply as a precaution, even if the burners are actually lit. This can result in your furnace starting the ignition process but failing to stay lit.
1. Will a furnace run without a flame sensor? No, a furnace will not operate without a flame sensor.
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.
Flame Sensor Lifespan
While your furnace may last about 15 to 30 years, a flame sensor won't last nearly as long. Flame sensors have an average lifespan of about five years.
If a flame sensor replacement is necessary, it's a low-cost fix that you can likely handle yourself if you feel comfortable working with the unit.
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.
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.
While the average life span of a flame sensor is about five years, many technicians recommend replacing the flame sensor a little more often at every two to three years. This schedule helps ensure that the flame sensor is always in good condition and not causing problems with the gas supply.
Pilot Lights and Flame Sensors Could Be the Issue
A modern furnace without a pilot light relies on flame detectors to ensure the successful completion of a heating cycle. If the flame detector is covered in dust, dirt, or grime, you will quickly lose heat and your gas furnace will start blowing cold air.
Without a flame sensor, your furnace will keep emitting gas even when there's nothing to ignite it, resulting in hazardous gas buildup.
Press and hold the test button on the smoke detector. It can take a few seconds to begin, but a loud, ear-piercing siren should emanate from the smoke detector while the button is pressed. If the sound is weak or nonexistent, replace your batteries.
Flame detectors are also effective in detecting fires in areas where smoke detectors would be prone to false alarms, such as kitchens, garages, and other areas with high levels of smoke or steam. Flame detectors are also less prone to false alarms than smoke detectors.
Located in front of the burners, it's a rod that juts out where the flame comes out of the burner. It's always on the opposite side of the ignitor as well. For instance, the flame sensor is on the left side, while the ignitor is located on the right side of the burners.
Most flame sensors have a life expectancy of about 20 years. Before reaching the end of its lifespan, the sensor will start to malfunction from natural wear. It's best to replace the sensor before it gets to that point.
Attach one wire from your multimeter to the flame sensor wire and the other one to the unit where you unplugged the wire. Turn on the unit. Look for a reading between . 5 and 10 micro-amps with the normal range between 2 and 6.
Gently pull the sensor out of its mounting position. Be cautious not to damage any surrounding components. Using steel wool or fine-grit sandpaper, gently scrub the metal rod of the flame sensor to remove any soot or residue. Be careful not to apply too much pressure or scratch the sensor, as this could damage it.
People tend to use the terms “flame sensor” and “thermocouple” interchangeably. In truth, while they basically perform the same job, they're not the same thing. If your furnace uses an electronic controller, it's got a flame sensor. Thermocouples are used on standing pilot furnaces that have pilot lights.
They will cost around $200 if it is done during regular maintenance service. Likewise, flame sensors can become too dusty and malfunction, but a thorough cleaning can restore them. However, if it's too late and you need to replace the flame sensor, expect to pay between $80 and $250.
Similar to a thermocouple, replacing a flame sensor can be a hard task and should usually be left to the pros.
If the flame sensor is clean but the burners still shut off around 6 seconds after ignition, this may be the result of a faulty ignition control. A common cause of a faulty ignition control which fails to sense flame is water damage.