The spider in the pilot tube
It sounds like folklore and it is the single most common gas fireplace fault we are called out for. Certain spiders are attracted to the odorant added to natural gas, and over a long warm season with the appliance idle they build webbing inside the narrow pilot orifice and tube.
The effect is a pilot that will not light, lights and immediately goes out, or burns a weak lazy yellow instead of a crisp blue cone. It has been documented for decades and it has a name in the trade, and Los Angeles gives it an ideal opportunity: eight or nine months of an unused appliance sitting in a warm garage-dry climate is exactly the condition it needs.
The fix is cleaning the pilot assembly, not replacing anything. It is usually a first-visit resolution.
The thermocouple or thermopile
If the pilot lights but goes out the moment you release the control knob, suspect the thermocouple. Its job is to sense that the pilot is actually burning and hold the gas valve open; when it weakens with age, it no longer generates enough signal to keep the valve up.
A related symptom on a millivolt system is a pilot that stays lit but a main burner that will not come on, or a remote and wall switch that have both stopped working. That points at the thermopile rather than the thermocouple. Both are inexpensive parts and routine replacements.
Log placement, and why sooting is a warning
Gas log sets are engineered assemblies. The manufacturer specifies where each log sits, and those positions keep the flame away from surfaces it should not be touching. Logs get moved — by cleaning, by curiosity, by a previous owner — and drifted logs cause flame impingement.
The visible symptom is soot: black deposits building on the logs or up the back wall. A correctly running gas set should not soot. When it does, combustion is incomplete, and incomplete combustion is also how carbon monoxide is produced. It is not a cosmetic complaint and it should not wait.
What to check before you call, and what not to touch
Reasonable things to check yourself: that the gas shut-off valve is actually open, that the pilot control is in the right position, that the wall switch or remote has working batteries, and that the propane tank is not empty if you are on propane.
What not to do: take the gas valve apart, drill out a pilot orifice, or run the appliance with a burner that is visibly sooting. If you smell gas at any point, leave the valve alone, ventilate, get out and call the utility from outside.
Everything else on this page is a routine annual service item, which is rather the point — almost every first-cold-night call we take was preventable by a service in September.
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Frequently Asked Questions
Yes, and it is cheaper than the emergency call it prevents. The burner ports, pilot assembly, thermocouple, glass and gaskets are all wear items, and the pilot in particular collects webbing over the warm months here. A service before the season starts is the whole point.
A faint burning-dust smell for the first few minutes of the season is normal — it is dust burning off surfaces that have sat idle. A sharp chemical smell, or any smell of gas, is not. Shut it down and call us.