What's the difference between a thermocouple and a thermopile?

A thermocouple produces a small millivolt signal, typically 20-30 millivolts, used only to hold the safety pilot valve open. A thermopile produces a much higher output, usually 300-750 millivolts, strong enough to power the main gas valve and any wall-mounted switch or thermostat. If your fireplace has remote or wall switch control, it uses a thermopile.

How do I know if my thermopile needs to be replaced?

Common signs include the pilot staying lit but the main burner not responding to the wall switch or thermostat, or the fireplace shutting off intermittently. A multimeter reading below the rated millivolt output (usually under 300mV on load) confirms the thermopile is weak and should be replaced.

How do I install a replacement thermopile?

Shut off the gas supply, disconnect the wire leads from the gas valve noting their polarity, and remove the old thermopile from the pilot bracket. Install the new thermopile so its tip sits directly in the pilot flame, reconnect the leads, and test for gas leaks with a soapy water solution before restoring service. If you're not comfortable working with gas connections, have a qualified technician handle the installation.

Thermopiles

Shop replacement thermopiles for gas fireplaces. A thermopile (different from a thermocouple) generates the millivolt power that operates your gas valve and any wall-mounted switch or thermostat, so a weak or failed one is a common reason a pilot-lit fireplace won't turn on.

Thermopiles

If your gas fireplace has a wall switch or thermostat that controls the flame, it relies on a thermopile - not a thermocouple - to generate the electrical power that opens the gas valve. Thermopiles sit in the pilot flame and convert heat into a millivolt signal strong enough to run the valve and any connected wall controls. When a thermopile weakens or fails, the pilot may stay lit but the main burner won't respond to the wall switch, or the system may shut down entirely.

Why Buy a Replacement Thermopile

Fixes the most common reason a wall switch or thermostat-controlled fireplace stops responding.
Far less expensive than replacing the entire gas valve or pilot assembly.
A simple, DIY-friendly repair that gets your fireplace running again fast.

What to Consider When Buying a Thermopile

Confirm your unit uses a thermopile (typically 300-750 millivolt output) rather than a thermocouple (20-30 millivolt output). They are not interchangeable.
Match the lead wire length to your existing part so it reaches the gas valve without strain.
Check the thread size on the pilot bracket fitting before ordering.
If you're unsure which part you have, the pilot assembly model number or a photo of the existing part will confirm the correct replacement.

Frequently Asked Questions

What's the difference between a thermocouple and a thermopile?
A thermocouple produces a small millivolt signal, typically 20-30 millivolts, used only to hold the safety pilot valve open. A thermopile produces a much higher output, usually 300-750 millivolts, strong enough to power the main gas valve and any wall-mounted switch or thermostat. If your fireplace has remote or wall switch control, it uses a thermopile.
How do I know if my thermopile needs to be replaced?
Common signs include the pilot staying lit but the main burner not responding to the wall switch or thermostat, or the fireplace shutting off intermittently. A multimeter reading below the rated millivolt output (usually under 300mV on load) confirms the thermopile is weak and should be replaced.
How do I install a replacement thermopile?
Shut off the gas supply, disconnect the wire leads from the gas valve noting their polarity, and remove the old thermopile from the pilot bracket. Install the new thermopile so its tip sits directly in the pilot flame, reconnect the leads, and test for gas leaks with a soapy water solution before restoring service. If you're not comfortable working with gas connections, have a qualified technician handle the installation.