How To Bypass Flame Sensor On Furnace? Essential Guide

Over time, flame sensors can get coated with carbon or other debris, causing problems with the burner not igniting properly. If this happens, it’s important to fix the issue right away to avoid any potential hazards.

In this blog post, we will know in detail the steps to bypass the flame sensor on the furnace.

What is a Flame Sensor?

How To Bypass Flame Sensor On Furnace

A flame sensor is a device that detects when a gas burner lights up in your furnace. It’s a vital safety feature for heating systems in many homes, as it can sense the presence of a flame and prevent the furnace from releasing gas if there is no ignition.

Why Would You Want to Bypass the Flame Sensor?

Flame sensors are an essential safety feature in gas furnaces, responsible for detecting the presence of flames in the burner assembly and turning off the gas valve in case of any trouble. 

However, faulty flame sensors can cause issues, including preventing the furnace from starting up or causing it to shut down during operation. 

This is where the possibility of bypassing the flame sensor may come in handy, although only as a temporary solution until a specialist can replace it.

How to Bypass the Flame Sensor on Your Furnace?

If you’re having issues with your furnace flame sensor, you may be wondering how to bypass it. 

Here’s a simple guide to help you bypass the flame sensor on your furnace:

Locate the flame sensor

The flame sensor is usually located near the burner assembly in your furnace. You’ll need to access it through the furnace’s access panel.

Clean the sensor

Before attempting to bypass the flame sensor, try cleaning it with emery cloth. This may solve the problem and save you the cost of a service fee.

Bypass the sensor

To bypass the flame sensor, you’ll need to disconnect it from the furnace and use a metal rod to connect the two wires. This will allow the furnace to continue operating without the safety feature of the flame sensor.

Test the furnace

Once you’ve bypassed the flame sensor, turn on your furnace and test it. If it starts and operates normally, the sensor was likely the cause of your problem.

Consider replacement

While bypassing the flame sensor may be a quick solution, it’s not a good idea to leave it bypassed permanently. If your furnace flame sensor is faulty, consider replacing it with a new one for safety reasons.

Step-by-Step Instructions for Bypassing the Flame Sensor

If your furnace flame sensor is damaged or malfunctioning, you may consider bypassing it temporarily. 

Here are the steps to do so:

Turn off the powerUnplug the furnace and all its parts.
Locate the flame sensorFind it near burners of gas furnaces. Then unscrew the wire attached to it from the bracket.
BypassConnect the two terminals on either side with a jumper wire.
Reconnect and turn on powerReinstall components and reconnect wires. Then reapply power to your furnace.
TestCheck if jumping over the flame sensor works. If not, try other options or get help.

Using Emery Cloth to Clean the Flame Sensor

If your furnace is not running optimally, a dirty flame sensor may be the cause. Cleaning it with emery cloth can restore its performance and keep your furnace running efficiently.

Here’s how:

  1. Turn off the power to your furnace as a safety precaution.
  2. Locate the flame sensor, usually near the burner assembly.
  3. Carefully remove it.
  4. Gently clean the metal rod on both sides with the emery cloth until it’s smooth.

Replacing a Faulty Flame Sensor

Ready to replace your faulty flame sensor? Here’s what you need to do:

  1. Turn off power.
  2. Locate the sensor and unscrew it.
  3. Inspect the surface for damage and clean with an emery cloth if needed.
  4. Replace the old sensor with a new one, secured with screws.
  5. Switch on the electricity and test your furnace.
  6. If any issues arise, consult a professional repairman.

Testing the Ignition and Flame Sensor

Checking your Ignition and Flame Sensor is essential for a safe and efficient furnace

Here are 5 easy steps to follow:

  1. Shut off the power supply.
  2. Find the Sensor using the owner’s manual or the internet.
  3. Take it off and inspect it for dirt and damage.
  4. Use a multimeter to see if there’s continuity between the two terminals.
  5. Reinstall the Sensor, switch on the power and test run the furnace.

Safety Issues with Flame Sensors

Flame sensors are a must-have for any combustion system. They detect flames and ensure fuel is burnt safely. 

But some people may look to bypass these sensors, to save time or money. This is very dangerous, as flame sensors stop explosions and fires.

Also, bypassing this safety feature can void the warranty on expensive equipment like furnaces and boilers. 

Insurance companies may not cover any damages caused by accidents due to tampering with safety devices.

When to Call an HVAC Technician To Diagnose a Flame Sensor?

When diagnosing issues with your HVAC system, it’s important to know when to hand over the job to a professional. 

Attempting to fix the system yourself could lead to more costly repairs down the line. 

A trained technician can properly diagnose the issue and provide an accurate solution to get your system back to good working order.

In addition to more serious issues, like faulty flame sensor or gas valve problems, there are other signs that indicate it’s time to call in a specialist. 

Signs of Other Furnace Problems That May be Causing Issues

Here are some important facts to remember:

Bizarre Noises

  • If your furnace is making peculiar or loud noises, it could be an indication that something’s wrong. 
  • Clanking or rattling sounds may suggest a loose part. Whereas, a shrill whistling could point to air flow blockades.

Yellow Flame

Your furnace’s pilot light should always be blue. If it changes to yellow or orange, this suggests that the fuel-to-air ratio is off and needs to be dealt with urgently.

Thermostat Issues

Problems with your thermostat can cause temperature inconsistencies around your home. If you’re adjusting your thermostat regularly and still not seeing results, think about having it checked by an expert.


Flame sensors are an essential safety measure for any gas furnace. If the sensor detects no flame, it shuts down the furnace to avoid fire from gas leakage. Faulty flame sensors, however, can cause your furnace to malfunction, leading to downtime and distress.