Quick answer
A gas fireplace that won't light usually comes down to one of four things: a pilot that is out or a thermopile too weak to open the gas valve (millivolt units), a dirty igniter electrode or flame sensor (electronic IPI units), dead batteries in the remote, receiver or wall control, or an appliance gas valve left off since summer. Check the batteries and the shut-off first; both are free.
Why won't my gas fireplace light? Start by working out which of the two ignition systems you have, because they fail differently. A millivolt fireplace has a small pilot flame burning all the time and needs no household power, while an electronic fireplace (IPI, for intermittent pilot ignition) sparks a pilot only when you call for heat. Look through the glass at the burner: a small steady flame with the fireplace off means millivolt.
Check this yourself first: batteries, switches and the gas shut-off
- Remote handset: replace the batteries, then confirm the display responds when you press On.
- Receiver box: a second set of batteries, commonly four AAs, lives in the receiver in the control compartment below the firebox or in a wall box. That compartment gets hot, so these fail and leak sooner than the remote's. Check its slider is on Remote, not Off.
- Wall switch or wall thermostat: battery-powered controls go blank; plain rocker switches on millivolt units corrode at the contacts.
- Appliance shut-off: a quarter-turn valve, or a floor or wall key valve, near the fireplace. Handle in line with the pipe means open. Many get closed in spring and forgotten.
- Gas control knob on a millivolt valve: it should point to On, not Pilot or Off.
- Other gas appliances: if the furnace and stove are also dead, the problem is the supply, not the fireplace.
If the pilot is out and you are comfortable relighting it, follow the lighting instructions on the plate inside the lower access panel exactly, including the five-minute wait to clear gas before each attempt. After a summer with the valve closed the pilot line is full of air, and it can take a minute of holding the knob before the pilot catches. If you smell gas at any point, stop and follow what to do when you smell gas.
Millivolt fireplaces: pilot out or a weak thermopile
On a millivolt unit the pilot flame is the power supply. It heats two sensors: a thermocouple that holds the pilot gas open, and a thermopile that generates the fraction of a volt needed to open the main valve when the wall switch closes. That gives three distinct failures.
- No pilot flame: the pilot blew out or the gas is off. Relight it once.
- Pilot lights but dies when you release the knob: the thermocouple is not holding. Why a fireplace pilot keeps going out covers that fault.
- Pilot burns steadily but the main burner ignores the switch: the thermopile output is too weak, or the switch and its wiring are eating what little voltage there is. A technician measures the thermopile with a meter and bridges the switch terminals at the valve to tell the two apart.
Electronic (IPI) fireplaces: dirty electrode or flame sensor
On an IPI unit, clicking with no flame points to the spark electrode or the gas, and a pilot that lights while the clicking continues points to the flame sensor. The module sparks, lights the pilot, and waits for the sensor rod to prove flame before it opens the main burner. A sensor coated in white oxide or soot never sends that signal, so the pilot sits there sparking and the burner stays dark. A cracked electrode insulator or a loose ground wire sends the spark somewhere other than the pilot hood.
IPI systems also carry a backup battery pack so they light in a power failure, and batteries left in that pack for years leak and corrode the holder. Whether a gas fireplace works in a power outage explains that side.
What months of sitting idle do to a pilot assembly
A fireplace that worked in March and will not light in October has usually been visited by spiders or dust. Spiders spin webs inside the pilot tube and the burner orifice, where a web the size of a pinhead is enough to starve the flame. Dust and pet hair settle on the pilot hood and bake on at the first lighting. The pilot ends up small, yellow and wavering, too weak to heat the thermopile or reach the sensor.
Clearing that means taking the glass off, pulling the logs, opening the pilot assembly and gas connections, then leak-testing and checking the glass gasket on the way back in. In Ontario that is work for a TSSA-licensed gas technician, not a homeowner job, and it is the core of an annual fireplace service.
Call now, and when repair stops making sense
- Call now: you smell gas near the fireplace with it off.
- Call now: the burner lights with a bang or a delay, which means gas is building before it ignites.
- Call now: there is soot on the glass or logs, or a carbon monoxide alarm has sounded.
- Book a visit: batteries, switch and shut-off all check out and it still will not light after one relight attempt.
Fireplace repairs are quoted in writing after the fault is found, because valves, modules and pilot assemblies vary by maker; the diagnostic visit is $90–$150 and is folded into the repair if you proceed. When the valve or pilot assembly for an older unit is no longer made, replacement is the practical answer, and a sealed direct-vent insert is the usual route. ZK Mechanical's TSSA-licensed technicians handle gas fireplace installation and service across Burlington, Oakville and Hamilton: call (647) 801-1252 or book a visit.