How to Bypass a Flame Sensor On a Furnace

The flame sensor on a furnace is a safety feature and bypassing it is too risky. In good conscience, we cannot teach you how to bypass a flame sensor on a furnace. Instead, we will give you a few tips for getting your flame sensor to work again. You may be in a tight spot with the cold winter freezing your home and these quick HVAC fixes might be just the thing to get you through the harsh elements.

What Is a Flame Sensor?

As mentioned, it is a safety feature built to detect a flame from the burner. If it cannot detect a flame, it shuts down the furnace to prevent gas from leaking into your home, which is very hazardous for obvious reasons. This is legitimately life and death we are talking about here.

Tips for “Bypassing” the Flame Sensor

First of all, are you sure it’s the flame sensor? Have you tried simply resetting the furnace? Start there and see if that works. Of course, if it is indeed the flame sensor that is the problem, then this will not work. If it didn’t, then it’s time to troubleshoot. Again, we are not technically bypassing the flame sensor. That is too dangerous. We have a different solution:

Remove the access cover on the furnace.
Locate the flame sensor.
Cut the power to the furnace.
Shut off the gas control valve.
Take out the flame sensor by removing the mounting screw.
Examine the part to see if it’s compromised, either by damage or dirtiness. If dirty, it just needs cleaning. If damaged, for example, the porcelain insulation is cracked, then it needs replacement. To clean it, use steel wool and lightly scrub it until you remove all traces of debris, rust, etc. Do the same for the electric igniter (if you have one).
Reinstall your new or cleaned flame sensor.
Turn on the gas valve and cut the power back on, and you’re back in business.

Get a New Flame Sensor Here at PlumbersStock

Now that you know you can't bypass a flame sensor and need to buy a new one, shop around PlumbersStock for the right replacement flame sensor. We offer the best pricing on furnace parts, including furnace ignitors, motors, blower wheels, etc. Did you know that you can find member pricing here on certain items (typically name brand, MAP priced items) if you log in? For industry professionals buying in bulk, please consider contacting us directly for extra special pricing and extra savings.