The sensor's failure to detect a flame causes the furnace to shut down as a safety measure. Inconsistent heating: A faulty flame sensor can cause the furnace to cycle on and off frequently, leading to inconsistent heating in your home. You may notice hot and cold spots or a lack of comfortable warmth.
If your furnace stops working properly, look for warning signs that your flame sensor has failed: Furnace burners turn on but go out after a few seconds. Soot and other debris is covering the end of the sensor (cleaning the flame sensor may fix this issue rather than a flame sensor replacement)
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.
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.
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.
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.
If you suspect the flame sensor is dirty or malfunctioning, cleaning it might help restore proper function. However, if you're unsure or uncomfortable performing maintenance yourself, it's a good idea to call a professional HVAC technician for a thorough inspection and service.
When the flame lights, you should read between 0.5 and 10 microamps (μA), depending on the furnace. Readings between 2 and 6 are common.
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.
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.
Flame sensors and thermocouples are both furnace safety components that sense heat and prevent gas leaks. However, the two parts function differently and are not interchangeable. Thermocouples are used in furnaces with pilot lights; flame sensors are used in furnaces with electronic ignitions.
Without a flame sensor, your furnace will keep emitting gas even when there's nothing to ignite it, resulting in hazardous gas buildup. If your flame sensor is dirty or faulty, it will automatically shut down the heating unit if it doesn't detect a flame.
Defective Igniter or Pilot Light
If it clicks but your furnace won't ignite after the combustion cycle, the electronic ignition systems probably need to be replaced. In cases where the furnace ignition starts normally but only stays on for a few minutes and then goes out, a new pilot light likely needs to be installed.
Similar to a thermocouple, replacing a flame sensor can be a hard task and should usually be left to the pros.
If the sensor is dirty, it may fail to detect the flame, causing your furnace to shut down. A professional HVAC technician should clean or replace the sensor if needed.
Recognize common symptoms of flame sensor failure: short cycling, frequent shutdowns, and specific error codes on the furnace display. Clean the flame sensor regularly using fine-grit sandpaper or steel wool to remove buildup and ensure proper functionality.
A heat exchanger replacement is often one of the most costly repairs in a furnace, and the expense can sometimes rival that of installing a new furnace. Typical replacement costs vary widely but can easily reach several thousand dollars, especially if labor costs are factored in.
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.