Gas Log Resource Center
Millivolt Gas Log Systems
Millivolt systems use a continuously burning standing pilot to generate a small electrical current — enough to operate the gas valve without any external power source. They are the most common ignition type in older gas fireplaces and log sets across Northeast Ohio.
What Is a Millivolt System?
A millivolt system has a standing pilot — a small flame that burns continuously, even when the fireplace is off. The pilot heats a thermocouple and thermopile, which generate a small DC voltage (measured in millivolts). This voltage powers the gas valve, allowing the main burner to be turned on and off without any external electricity.
The thermocouple is a safety device: it holds the gas valve open only as long as the pilot is lit. If the pilot goes out, the thermocouple cools, the voltage drops, and the gas valve closes automatically — preventing unburned gas from accumulating.
The thermopile generates more voltage than the thermocouple and is used to power wall switches, remote receivers, and thermostats. A healthy thermopile typically produces 300–750 millivolts. Low thermopile output is one of the most common causes of millivolt fireplace problems.
Millivolt vs. IPI
Advantages
- No external power required — works during power outages
- Simple, proven technology with decades of field history
- Fewer electronic components than IPI systems
- Compatible with wall switches, remotes, and thermostats
Limitations
- Standing pilot burns continuously — higher gas consumption than IPI
- Pilot can be extinguished by drafts or debris
- Thermocouple and thermopile wear out over time
- Older technology — fewer smart-home integration options
Millivolt System Repair in Northeast Ohio
Thermocouple and thermopile replacement are among the most common millivolt repairs OGF performs. A failing thermocouple causes the pilot to go out shortly after lighting; a weak thermopile causes the main burner to fail to open or the remote receiver to malfunction.
OGF stocks thermocouples and thermopiles for most common fireplace and gas log set models. Most millivolt repairs can be completed in a single visit.
Common Questions
My pilot lights but goes out when I release the button — what's wrong?
This is almost always a failing thermocouple. The thermocouple needs to reach operating temperature before it can hold the gas valve open. If it's worn out, it won't generate enough voltage. OGF can replace the thermocouple in a single visit.
My pilot stays lit but the main burner won't come on — what's wrong?
This usually points to a weak thermopile or a faulty gas valve. OGF tests thermopile output with a multimeter — a reading below 300mV typically indicates replacement is needed.
How often should I replace the thermocouple and thermopile?
There's no fixed replacement interval — they last until they fail. Most thermocouples last 5–10 years; thermopiles vary. OGF tests both components during annual inspections and replaces them when output is marginal.
Millivolt Fireplace Not Working?
Thermocouple and thermopile replacement are quick, affordable repairs. OGF stocks common parts for same-visit service.