Gas Fireplace On/Off Wall Switch Not Working: FIXED

Gas Fireplace On/Off Wall Switch Not Working

Gas fireplaces with wall switches often fail to light the main burner even when the pilot flame is turned on.

This is one of the most common problems homeowners face. If you’ve come across this issue and are looking for solutions, you’ve come to the right place. 

This blog article will teach you how to troubleshoot and repair a faulty gas fireplace wall switch.

Why is Gas Fireplace Wall Switch Not Working?

So, why would a gas fireplace wall switch stop work? Let’s begin by explaining how a gas fireplace works.

The pilot light ignites the thermocouple/thermopile sensor, which is then heated up, resulting in small amounts of electric energy. 

A switch on the wall receives this voltage. Turning the switch to the ‘ON’ position sends the same voltage back to the fireplace, signaling it to turn on.

But then there’s a possibility that the wiring inside the switch will degrade over time because of corrosion, dirt build-up, and physical wear; as a result, the switch loses electric voltage, and in response to the switch being turned on, a reduced voltage is delivered back to the fireplace, which does not trigger it to start the main burner.

Do not worry. Here are three major problems and ways to fix a gas fireplace wall switch. 

Depending on what’s wrong with it, you’ll know how to fix it. 

Corroded Wirings 

Corroded/damaged wires are the most common problem. This usually happens because the wiring inside the switch degrades over time because of corrosion, dirt build-up, and physical wear.

You can check if the wiring is damaged by following a few steps. They are as follows:

  1. Using a screwdriver, remove the switch cover plate and the switch itself. 
  2. Make sure the terminals are not loosely connected. 
  3. Check the connections and see if the fireplace works. 
  4. Reinstall the wall switch and redo the flat screws. 

That’s it. Most likely, this should work, but if the wire is faulty, then it’s a whole different story.

The gas valve wire will need to be bypassed in that case. Here’s how.

  1. Open the control panel of your gas valve. 
  2. Locate two terminals called ‘TH’ and ‘TP’. 
  3. Take a jumper wire, a paper clip, or a small insulated wire. Put the bare ends of it into the terminals from the previous step. 
  4. Try turning on the fireplace as usual. If it works, then a faulty wire is confirmed. 

This method can be used to detect damaged wires, and the next step is to replace them.


It is simply a matter of replacing the wiring that will solve this problem. It is important to note that the wire gauge used for connecting the fireplace wall switch must be 18 AWG. It cannot be larger or smaller. 

We strongly recommend you purchase the following wires if you haven’t already:

Did you get them? Well done, now follow me in these steps.

  1. You should connect the wires to your fireplace’s “TH” and “TP” terminals to ensure it operates properly.
  2. Insert the wire’s opposite end into the grommet.
  3. A hacksaw should insert the wire into the drywall/wall. A switch can be installed directly instead of using gang boxes.
  4. Connect the wires to the switch with flat screws.
  5. Check the connection by turning the fireplace on once.
  6. To close it, screw the switch into the wall.

Damaged Millivolt Switch 

Next, and the most obvious problem, is whether the switch has been damaged. There isn’t a lot of attention paid to fireplace wall switches so that they could go bad quickly. In that case, the fireplace won’t work. 

The switch is faulty when the circuits are closed, and the thermopile works! 

Bypass the fireplace wall switch and check if it has gone bad. Here’s how

  1. Unscrew the cover plate from the wall switch.
  2. Once the switch pops out, double-check if it’s the fireplace wall switch or not. Wires connected to it will be thinner than normal electric wires (fan, light, etc.). If not, it’s not the fireplace switch. 
  3. Remove the wire from the switch by unscrewing the terminal screws that hold the wires to the switch. 
  4. Twist the wires a few times. This way, the switch is bypassed, and the circuit is closed. 
  5. Turn on the fireplace with the pilot light and ignition switch. The wall switch is gone if it works.


There is no in-between; you must replace the millivolt switch to resolve this issue. Wondering what a millivolt switch is? 

A millivolt switch works on millivolt circuits, like gas fireplaces, unlike a 120V switch. You noticed that fireplace switches have thicker wires than other electric appliances. 

Here are the instructions for replacing the fireplace switch:

  1. Turn off the pilot and ignition of the fireplace.
  2. A 15-foot wire should be used to connect the switch to the gas valve. It is not necessary to perform this step if you are replacing a switch that already has wires installed.
  3. The wires can be removed by unscrewing the terminal screws.
  4. Spade terminals provide a secure connection, so attach them if you can. Give the wire ends a twist and inserts them into the terminal screws.
  5. Connect both sets of flat screws after reattaching the switch. For the switch frame, use one set, and for the switch cover, use the other.

Switch not getting enough Voltage

‘Millivolt loss’ is the reason for the problem. 

Thermopiles should produce 350 to 1000 millivolts and send them across the switch. Voltages under 350 mV indicate a problem. 

If your switch and wiring are fine, a lack of voltage can be caused by two things: 

  1. A decayed or dirty wire. 
  2. A dirty thermopile. 

Find out which of these two reasons you’re suffering from. For this, you’ll need a digital multimeter.

Find out why your gas fireplace thermopile or wire is losing millivolts. 

  1. Set the pilot light on for 2 minutes. 
  2. Remove the wall switch and locate the terminals. 
  3. Bring out the wire. 
  4. Set the multimeter to DC millivolts. 
  5. Connect the black and red leads from the multimeter to each switch terminal. Start the ignition switch to run electricity. 
  6. The multimeter will read and display the millivolt. Note this and call it Switch Voltage.
  7. Wire leads back to terminals and resets the switch. 
  8. Mount the multimeter leads on the control valve’s TH and TP/TH terminals. 
  9. The voltage will be read. Write it down as ‘Thermopile Voltage’. 


Taking basic care like cleaning the wires when ( Switch Voltage < Thermopile Voltage)

In case you notice significant millivolt losses across the wire, try this. When the switch voltage is 150 MV, and the thermopile voltage is 750 MV, you must clean the wire so it can conduct electricity. 

It is okay for the thermopile to drop about 120-100 MV to the switch, but any more significant drop indicates dirty or corroded wires. 

A 120V high-voltage wire can prevent dirt/corrosion from building up. However, millivolt circuits are not like that. Over time, it’s pretty common to have a dirty wire blocking the voltage needed to open the gas valve. In addition, copper wire loses its ability to conduct electricity correctly due to oxidation and chemical reactions. 

To clean up corroded or dirty copper wire, follow the steps: 

  1. Disconnect both ends of the wire. One from the switch terminals and another from the control valve. 
  2. Cut off the old ends of the wires and bring out a few new ones. On both the switch and control valve ends, do this. 
  3. Take a steel wire brush and scrub the open ends of the wires. 
  4. The wires can be rejoined once the contact points have been restored. 

The other solution is to

Clean The Thermopile (If Switch Voltage = Thermopile Voltage)

The problem is with the dirty thermopile if the switch and thermopile voltage are low (lower than 350 MV). Since it’s close to the fire area, it’s likely to be clogged by soot, dust, and dirt. This will reduce its electric conductivity. 

Cleaning it up will restore voltage loss, allowing the wall switch to function again. 

Here’s how to do it

  1. Turn off the gas supply. 
  2. Detach the wires around the thermopile, especially the TH and TH/TP terminals. 
  3. Blow the terminals gently with an air blower to remove loose dirt and dust. 
  4. Use a stainless steel brush and fine-grit sandpaper. Use a small brush (about 150-200mm in length).
  5. To clean the thermopile, use sandpaper and a wire brush to remove soot and sticky dirt. Just looking at it will tell you how much dirt has been removed. 
  6. Reread the multimeter reading to see if the problem has been resolved. 750-1000 MV is the magic number! 
  7. Reconnect the wires to the TH and TH/TP terminals after cleaning. 

Heat n Glo Wall Switch not Working 

In most cases, Heat n Glo fireplaces buyers report intermittent wall switches. Sometimes you turn it on, and the fireplace’s main burner will come on. There are times when it won’t light up. 

This issue is primarily caused by corrosion of the contacts inside the wall switch. If it is already corroded, try repeatedly turning the on and off switches. 

Open the switch’s cover plate, unscrew the switch to access the wiring, and clean the wires and connectors with denatured alcohol and steel wool. It should knock off corrosion and prevent millivolt loss.


Although you might face some issues with your gas fireplace, the On/Off Wall Switch. But after determining the main issue, some basic steps can be taken to resolve them

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