If you have a furnace, you might ask yourself if there’s a way to bypass/trick/jump out the flame sensor when the flame is present due to shutting down the furnace. Flame sensor problems are some of the most common reasons homeowners contact HVAC technicians. The following information will help you understand if you can bypass the flame sensor and how to replace and clean it.
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Where is the flame sensor located?
You will find the flame sensor behind the access panel of the furnace. Most of the time, you must remove several screws or tabs to put the board aside. The flame sensor is a metal rod with either white or yellow /brown porcelain around the base. This is what you will see after you remove the panel.
The flame sensor is installed outside the burner assembly and has one wire attached. Its sensing stick is placed inside the fire chamber or burn box. Some sensors are straight, whereas others have a bent end (to 45 or 90 degrees).
How can you bypass a flame sensor temporarily?
Some furnace technicians claim they know how to bypass the flame sensor on some furnaces, but we need to highlight that you cannot do it on new furnaces. Bypassing safety controls such as the flame sensor, even if possible, doesn’t serve much. To properly troubleshoot the flame sensor, you must use a meter or instrumentation.
Some may think bypassing the flame sensor when it has gone wrong and doesn’t perform as it should is the solution. After all, it’s pretty common to trick or jump around the issue when managing mechanical appliances. Even if it works in theory, you can make the furnace run after bypassing the flame sensor.
Even if possible, it’s not a good idea to bypass the flame sensor simply because it is a crucial safety feature on the furnace.
How do you know that a flame sensor has gone wrong?
It would help if you didn’t attempt to repair the flame sensor unless you know it has broken. Replacement is another solution and here are the signs that something’s wrong with the flame sensor:
- The flame sensor’s porcelain is broken or cracked. You can quickly notice this when taking a look at the flame sensor. You might have to unbolt and remove it for proper examination.
- The furnace lights up but turns off rapidly because the flame sensor doesn’t detect heat.
- There is corrosion or heavy soot on the flame sensor.
An error code may signal that the flame sensor requires cleaning or replacement. With most furnace models, the error code is blinking, or there’s a solid light on the furnace. The codes can be numbers, a combination of numbers and letters, or flashing lights. The unit will show the “Lockout” error code if the flame sensor is flawed in some furnaces.
You can start by switching out the flame sensor is an effective maintenance method as the flame sensor is relatively cheap ($6 to $75, depending on the brand). You can only buy the flame sensor or the whole assembly, but most are more affordable than $40.
Cleaning the flame sensor
When the flame sensor doesn’t work correctly and you know your way around mechanics, you can clean or replace the flame sensor. You will save anywhere between $65 and $150, which is the service fee for certified HVAC technicians to come and clean or replace the flame sensor.
If you decide to clean the flame sensor on your own, here are the steps to follow:
- Shut off power and gas to your furnace
- Remove the mounting screw and place it in a safe place
- Remove the sensor
- See if there are any cracks. If you notice cracks, replace the flame sensor (details below).
- Use an emery cloth to clean away soot and corrosion from the flame sensor carefully
- Reinstall and fasten the flame sensor
- Turn the power back on to the furnace and give it a run
Replacing the flame sensor
If you cannot see results after cleaning the flame sensor and the furnace still doesn’t remain on, you should replace the flame sensor. Here’s what you need to do to replace the flame sensor safely:
- Find out the rating of the current flame sensor. You can also take with you the flame sensor when looking for a new one in the HVAC parts store
- Shut off the power and gas to the furnace
- Remove the mounting screw
- Carefully pull out the flame sensor
- Detach the wire from the sensor
- Push the new sensor into the opening
- Use the mounting screw to secure the sensor
- Attach the wire to the new sensor. See if the connection is tight. Sometimes, you might have to squeeze it together with pliers carefully
- Restart the furnace
Are flame sensors expensive to replace?
The cheapest solution is to clean the flame sensor. A $5 emery cloth is everything you need to clean the flame sensor—it couldn’t get more affordable than that.
If the flame sensor isn’t dirty but broken or cracked and needs replacement, you can get a new one for anywhere between $6 and $75. You can find flame sensors online or from home improvement stores. You have to ensure you buy the proper flame sensor for your furnace. Universal flame sensors are also available or buy an OEM (original equipment manufacturer) part.
When you don’t think you have the skills, patience, or equipment to clean or replace the flame sensor, you should call the certified HVAC technicians. The minimal service fee varies from $65 to $150 and you need to add the price for the flame sensor as well. You will still pay the service fee if the flame sensor only requires cleaning. Once you learn how the professionals do it, you will be able to do it on your own next time.
Is it possible for a furnace to perform without a flame sensor?
The flame sensor is crucial to a furnace’s operation and it does what it says: it detects if there’s a flame. When there is a flame, the furnace runs, and the gas burns; when the sensor doesn’t detect any flame, a gas leak might be the problem.
When the thermostat sends a command for heat, the furnace’s draft motor comes on and the igniters heat up shortly after (it takes a few seconds). The gas valve will open to eliminate gas and there will be a flame. The flame sensor has to detect the flame. It’s how the furnace operates correctly and heats the house as it should.
When the flame sensor doesn’t work, the furnace will automatically shut down and won’t release gas. If there is no flame sensor and no flame, the gas will keep flowing without being burned. Therefore, an explosion will take place shortly after.
All things considered, the furnace cannot operate without the flame sensor. The flame sensor is there for a reason, to keep you and your family safe and your furnace able to properly heat your home.
