Pilot flame
The pilot must contact the sensing device correctly. A weak, dirty or misdirected flame reduces output.
FIREPLACE KNOWLEDGE BASE
Why a gas fireplace will not stay lit
The answer starts with the sequence of operation. A technician needs to know which type of ignition system you have, what the controls are asking for, and where the sequence stops.
SEQUENCE OF OPERATION
MTWO COMMON SYSTEM TYPES
Millivolt or electronic ignition?
The diagnostic path changes with the control system.
Standing pilotThermocouple or thermopile creates a small electrical signal
Electronic ignitionControl module starts and proves the ignition sequence
Safety responseGas closes when flame is not proven
START WITH THE SYSTEM TYPE
Standing-pilot fireplaces use flame-generated electricity.
A properly shaped pilot flame heats a thermocouple, a thermopile, or both. Those devices generate a small electrical signal. The signal helps hold the pilot safety open and, on millivolt systems, supplies the gas-valve circuit used to start the main burner.
Signal is generated
The thermocouple or thermopile converts heat from the flame into a small DC voltage.
Call for flame
The wall switch, remote receiver and wiring complete the main-burner circuit.
Main valve opens
The gas valve opens only when the safety and operating conditions are satisfied.
MILLIVOLTS MATTER
“750 mV” is a device rating, not a universal pass number.
Many fireplace thermopiles produce roughly 400 to 750 millivolts with no load when the pilot flame heats them properly. The exact acceptable reading depends on the appliance, the test points and whether the circuit is open or carrying a load.
A reading that looks acceptable with no load can collapse when the valve circuit is connected. Excess resistance in a switch, remote receiver, connector or wire can also prevent the main valve from opening.
Thermocouples work at a much lower voltage and usually hold the pilot safety magnet. They do not use the same test range as a thermopile.
WHEN IT WILL NOT STAY LIT
More than two faults are possible.
A bad thermocouple, thermopile or gas valve is possible. A proper diagnosis also checks the conditions surrounding those parts.
Pilot flame problem
Dust, restricted pilot openings, improper flame shape or low gas pressure can keep the sensing device from heating correctly.
Weak thermocouple or thermopile
Output can be low from age, contamination, poor flame contact or failure under electrical load.
Switch or wiring resistance
Wall switches, remote receivers, connectors and long wire runs can consume part of the small millivolt signal.
Gas-valve fault
The safety magnet or main-valve operator can fail, but the valve should be condemned only after the correct input and circuit conditions are verified.
Gas supply or pressure issue
Incorrect inlet pressure, regulator trouble or another supply problem can affect pilot and main-burner operation.
Venting or safety response
Blocked venting, spillage or an oxygen-depletion safety response can shut some appliances down. This needs professional attention.
ELECTRONIC IGNITION
Spark-ignition fireplaces follow a controlled sequence.
These systems use an ignition module or integrated control. The flame signal is usually measured as flame-rectification current, not thermopile millivolts.
Call for heat
The wall control, remote or thermostat sends a request to the ignition control.
Safety checks
The module checks the required switches and operating conditions for the model.
Spark and gas
The module energizes the ignition sequence and opens the appropriate gas-valve stage.
Flame proof
The flame sensor proves flame. If flame is not proven, the module closes the gas valve and can retry or lock out.
Safety: do not bypass a flame sensor, pressure switch, spill switch, limit, ignition control or gas valve. If you smell gas or a carbon monoxide alarm sounds, leave the building and call 911 or the gas utility from outside.
CUSTOMER QUESTIONS
What the symptoms tell us.
The pilot stays lit, but the main burner will not start. What does that mean?
The thermopile output under load, wall switch, remote receiver, wiring, connections and gas-valve circuit all need to be tested. A lit pilot does not prove the main-burner circuit is healthy.
The fireplace lights and then shuts off. Is the gas valve bad?
It is one possibility. Flame sensing, pilot quality, venting, safety controls, gas pressure and electronic-control faults also cause shutdowns.
Why is sequence of operation important?
Each step must happen before the next one. Finding the exact step where operation stops prevents replacing parts without proof.
Does maintenance include repairs?
No. The $199 maintenance service covers its listed cleaning, inspection and testing scope. Parts, repairs and extra diagnostic work are separate and require approval.
READY BEFORE THE HOLIDAYS
01
Request maintenance
Use the fixed-scope fireplace maintenance page.
02
We test the operation
The pilot, controls, flame and accessible components are checked.
03
Approve repairs separately
No repair or part is added to the maintenance price without approval.