How To Fix Gas Fireplace – NO FLAME Problem

Typical Cost To Install New Furnace Average: $4,160 - $5,730
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Most fireplaces are pretty “primitive” and only have a few components that can malfunction and will require repair.

Therefore, finding why you have no flame in your gas fireplace is pretty straightforward. The most complicated, expensive to buy and/or replace part is the gas valve. The good news is – gas valves almost never fail!

According to John – a Quadra-Fire fireplace service technician out of Norwood MA, who does 4-7 house service calls every day, he only had to replace 5 gas valves in more than 10 years. That’s 1 valve every 2 years!

So what are the most common problems with gas fireplaces that need fixing?

1) Thermocouple

Thermocouple is a device keeps your pilot light lit. If you have no pilot light, it is most likely that your thermocouple is bad, and needs replacement. Thermocouple are pretty universal and cost $12-$35.

How thermocouple works? Thermocouple is a low voltage “generator” that creates 25-30mv of DC electricity, that keeps the pilot gas valve open. When thermocouple is heated by pilot flame, it begins to make electricity. If pilot light is out, there is no power to keep the pilot valve open.

Thermocouple and Thermopile on a Gas Fireplace

Thermocouple and Thermopile on a Gas Fireplace with lit pilot light

2) Thermopile

Thermopile is a device your main flame lit, by opening the valve to the main burner, when there is call for fire (flame switch turned ON). Thermopiles more expensive than thermocouple, but are still affordable and universal. Thermopiles cost $20 – $60 for a quality brand name part.

How thermopile works?

Thermopile is a low voltage “generator” that creates 650-800mv of DC electricity, that keeps the main burner gas valve open. When thermopile is heated by pilot flame, it begins to make electricity. If pilot light is out, there is no power to keep the main burner valve open.

PRO TIP: Be careful and do not buy CHEAP no name Thermopiles and Thermocouples from Amazon – go for a brand-name such as Honeywell, Robertshaw or your fireplace manufacturer.

Most cheap thermopiles will have weak power output (below 400mv) and will cause intermittent flame problems that will be hard to diagnose, because you will assume that your thermopile is GOOD, and problem is elsewhere.

How I Found a Problem In My Fireplace [VIDEO]

Below is a step by step video of troubleshooting my fireplace with no flame, going through thermocouple, thermopile, verifying that gas valve is good, high limit switch are good, and finding that it was all due to an old ON/OFF switch that costs $3.50 …

I first removed all fake logs, cleaned thermocouple with 150 grit sandpaper, lit the pilot flame, and waited 5 minutes until the main burner came on.

This indicated that VALVE, Thermopile and Thermocouple were all good. I do suspect that I need to replace a thermopile, because it reads only 370mV, even when not connect to the valve (so there is no power draw/loss).

Next I jumped bot contacts of on/off switch and flame came right on!

Next I unplugged the ON/OFF switch, and connected wires directly – flame came right on again, which means High-Limit switch is good, and it was the on/off switch!

Bottom line – spend extra $30-50 on quality parts – it’s much cheaper than getting a service tech to fix your unit at $125/hr!

Troubleshooting a Gas Fireplace

1) If there is no pilot flame, thermopile won’t sense heat and won’t open the valve.
2) If there is a pilot flame, but main flame does not come on – most likely it is one of the three following issues:

Bad thermopile: If your thermopile is bad, it won’t generate enough heat to open main burner flame.

You can test your thermocouple and thermopile with a quality digital voltmeter. Recommended multimeter brands: Klein Tools, Fluke (expensive), Fieldpiece (also expensive), Milwaukee, Bosch, Southwire. Stay away from cheap or no name brands, with 100s of fake 5-star reviews on Amazon.

Set your meter to VOLTS DC, and range to mV (millivolts). You can heat up your thermocouple / thermopile with a lighter for 30-45 seconds, and keep it hot. While flame is still going, put meter lids on the connectors of thermopile.

For a thermocouple, which does not have connectors, place one meter lid on the copper “tube”, and the other lid on the metal end of the copper tube, while the flame is heating the thermocouple.

Your thermopile voltage should be between 650mV and 800mV.
Your thermocouple voltage should be between 25mV and 30mV.

It’s not the thermocouple or thermopile (pilot light is ON) – what’s next?

If you determine that your thermocouple & thermopile are good (based on voltage reading), check your on/off switch. Easiest way, is to light the pilot light and wait 5 minutes.

Then take a jumper cable, or a piece of 14/12 ga wire with stripped ends, and connect two contacts, where THERMOPILE is attached to the Gas Valve:

Jumping & bypassing on/off switch

If flame comes on, it is either bad ON/OFF switch or bad/stuck High Limit Switch.

Next step after you got flame by jumping the on/off switch:

Unplug the on/off switch, and connect the wires together. If you got flame, it is bad switch. Else, it’s a bad high limit switch.

That’s it! -Your are now a master fireplace serviceman 🙂


Working with Gas and Electricity is very dangerous and should only be done by licensed plumbers / gas fitters / electricians.

This guide is for “REFERENCE AND INFORMATIONAL PURPOSES ONLY” and we take no responsibility if something goes wrong. By following steps in this guide, you assume ALL THE RISK!

About Leo B

Leo has been a contractor since 2003, specializing in: roofing, siding, general contracting (GC) and residential remodeling. Leo is also a Certified HVAC, Oil & Gas Heating Technician/Installer. In addition to roofing and remodeling, Leo is passionate about Solar, green building and energy conservation, so a lot of my time and energy goes to installing energy efficient heating and cooling systems.

See more about Remodeling Calculator team here

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