Why the pilot won't stay lit

Nine times out of ten it is the thermocouple, the thin metal probe that tells the gas valve the pilot is actually burning.

The thermocouple sits right in the pilot flame. Heat makes it put out a tiny voltage. That voltage is what holds the gas valve open. Once it wears out, the valve reads the pilot as dead and shuts the gas the moment you release the knob.

A thermopile does the same job on newer millivolt systems. It runs the whole burner off that flame, so when it fails the fire quits, pilot and burner together.

Both are cheap parts. The skill is cleaning the pilot orifice, setting the flame so it wraps the probe, and reading the millivolts on a meter before we call it fixed.

Yellow flames, dead remotes and the rest

A gas fire should burn mostly blue. Lazy yellow flames and soot mean the burn is off, and off can mean carbon monoxide.

Some yellow tips are normal on a decorative log set. A burner that is all yellow, sooting the glass and the logs, is starved for air or running rich. The usual cause is simple. A log got knocked out of place.

Ceramic logs sit in an exact pattern the maker set. Move one and the flame hits it wrong, cools, and starts making soot and carbon monoxide. We put the logs back to the layout for that model and clear the ports.

Then there is the electronics. A piezo igniter with a cracked electrode clicks but never sparks. Battery packs die. Millivolt receivers and handheld remotes drop out, and wiring works loose behind the log set. We trace it to the actual break.

What we do on a gas fireplace visit

1. Test the gas

   A manometer goes on the line and we confirm the pressure before touching a part. Wrong pressure looks like a dozen other faults.

2. Check the safety chain

   Thermocouple or thermopile millivolts, the gas valve, the igniter. A meter tells us which link is broken.

3. Clean the burner and pilot

   The ports, the pilot orifice and the air shutter get cleared so the flame burns blue and even.

4. Reset the logs

   Ceramic logs go back to the manufacturer layout so the flame stops hitting them and sooting.

5. Check the vent and test for CO

   Flue clear, damper open, draft pulling. We confirm no carbon monoxide is spilling into the room before we leave.

Why venting and carbon monoxide belong in every gas call

A gas fire that cannot vent pushes carbon monoxide back into the room, and you cannot see it or smell it.

Gas logs in a masonry fireplace go up the same flue a wood fire uses. Block that flue with a bird nest, a shut damper or fallen debris, and the combustion gas has nowhere to go but back inside.

That is why the flue gets checked on every gas call. A camera up the chimney, a look at the damper, a draft test at the firebox. It takes a few minutes and it is the part nobody should skip.

Direct vent and B-vent units run their own sealed path to the outside. Those pipes and seals get inspected too. Nothing about gas is worth guessing on.