What the pilot is telling you, what you can safely check in five minutes, and when to stop and call.
You hold the knob in, the pilot lights, you count to thirty, you let go, and it dies. Or it holds, you turn the knob from PILOT to ON, and the pilot drops out the moment the main burner tries to light. Either way, the fireplace is telling you one specific thing: the safety circuit that proves the pilot is burning isn't satisfied.
In Houston this is the most common fireplace call we get from October through January, and the cause is usually the same. The fireplace sat unused for eight or nine months while humid air worked on the pilot assembly, the thermocouple, and the valve. Gas fireplace repair is our core business, so we've seen every version of this. Here's how to tell which one you have, what's safe to check yourself, and when to stop.
A standing-pilot fireplace has a small sensor sitting in the pilot flame. On most fireplaces it's a thermocouple, a copper rod that makes a few millivolts of electricity when it's hot. That tiny current holds a magnet open inside the gas valve. Hold the knob in and you're holding the valve open by hand while the thermocouple heats up. Let go too early, or let go with a thermocouple that isn't making enough power, and the magnet drops, the valve closes, and the pilot goes out.
That's the whole system. So "pilot won't stay lit" always comes down to one of three things: the flame isn't heating the sensor properly, the sensor isn't making enough power, or the valve isn't holding even though the power is there.
Fireplaces with a wall switch or remote also have a larger sensor called a thermopile that runs the main burner. It can be weak while the pilot holds fine. That's why "pilot stays lit but the burner won't come on" is a different problem with a different fix.
Here are the causes, in the order we find them in Houston homes.
One more thing to know about vent-free log sets. On a vent-free set, the pilot is an oxygen depletion sensor (ODS) and it is not adjustable. If an ODS pilot won't stay lit, the assembly gets cleaned or replaced, never bent or tuned. Anyone who offers to "adjust" one is guessing with your safety.
Five minutes, nothing that needs tools.
That's the list. If the pilot still won't hold after those five, nothing else you can do from the living room will change it. Thermocouple testing, pilot assembly replacement, and valve work need a meter, the right part for your model, and a leak check afterward. That's a service visit, and it's a short one.
Stop if any of these are true:
$185 service visit · $75 return trip if a part is needed
The visit covers the diagnosis and the repair labor. If a part is needed we quote it before ordering. Most pilot problems are fixed on the first visit with a cleaning and adjustment.
A Tanglewood homeowner with a Superior direct-vent fireplace called this month because the pilot would hold in PILOT but drop every time the knob went to ON. We cleaned and checked the pilot flame, then replaced the SIT pilot assembly, which is the right first move. It still dropped at ON. That narrowed it to the gas valve's magnet, so the valve became the second trip. Two visits instead of one, but no guessing and no parts bought that weren't needed. That's the order we always work in: flame first, sensor second, valve last.
Need the full picture of what we repair and what an annual tune-up includes? See our gas fireplace repair and service page, or browse the gas log catalog if your set is past saving.