Gas Burner Lights Then Dies, Pilot Stays Lit

The Short Answer: The pilot is holding. The main burner whooshes on, then drops. That is a thermopile sagging under load, a gas valve that will not keep the main operator open, rollout/ECO, or a packed FVIR screen — not a thermocouple if the pilot stays. Smell gas, leave. Hire a licensed plumber.

Search Intent & The Real Problem

You can see the little blue pilot through the view port. You turn the knob to ON, the main burner lights with a thump, runs eight to forty seconds, then goes dark. The pilot is still there — or it dies only after the main loads it. That is not the same job as a heater that will not stay lit when the pilot itself will not latch. This page is pilot holds, main will not hold.

What other guides get wrong

They send you to sandpaper a thermocouple. If the pilot stays lit after you release the knob, that thermocouple already proved flame to the pilot solenoid. They also skip millivolts under load — a thermopile can look fine with the main closed and collapse the instant the operator opens. They call it “air in the line” on a tank that heated water yesterday. Air is an install/relight problem, not a weekly dropout.

Step-by-Step Troubleshooting

Step 1: Split pilot-drop from main-drop

• What to look for: A standing-pilot knob with a live pilot after you let go, then a main that will not stay. No view port and a spark module is not this job.
• Required tools: Flashlight, phone photo of the gas-valve sticker and rating plate.

Rheem, Ruud, and Richmond share millivolt/electronic FVIR controls. Bradford White ICON does not. Wrong generator, no main.

Step 2: Thermopile millivolts — open circuit vs under load

• What to look for: A healthy thermopile (powerpile) makes hundreds of millivolts, not 20–30. Open-circuit is often in the 500–750 mV range. Closed-circuit with the main still off is lower. The number that matters is with the main open: if it sags under the valve’s dropout (commonly around 180 mV on millivolt operators — confirm that valve’s spec), the main dumps and the pilot may stay. Correct millivolts and a main that still will not hold is the valve.
• Required tools: Millivolt meter if you are qualified. Eyes on a sharp blue pilot wrapping the generator tip. No fitting wrenches.

A lazy yellow pilot will not drive a thermopile. That is orifice, lint, or low pressure — not a new valve. A Rheem that will not hold a pilot is the other half of this family; if your pilot is solid, do not buy that thermocouple.

Step 3: Rollout, ECO, FVIR, and the closet — before the valve

• What to look for: Soot on the combustion door, scorched paint at the opening, a rollout switch (bimetal on the door) that opened. Jacket too hot at the top — ECO on the control. Lint packed in the FVIR flame-arrestor under a post-2003 natural-draft tank. Dryer, range hood, or bath fan starting at the same moment the main drops (negative pressure stealing the chimney). Tissue at the draft hood should pull in with the burner on; if it spills, shut it down. Spillage is not “white smoke” you ignore.
• Required tools: Eyes, gas off to inspect the arrestor from outside. Do not pull an FVIR burner door if you cannot reseal it.

A perfect thermopile cannot hold a main that the chimney is blowing out, or that a rollout switch is killing. A heater that turns off by itself after a safety opens is the same physics with a different search.

Step 4: Gas supply without opening the pipe

• What to look for: Appliance shutoff handle parallel to the pipe (open). Other gas appliances lighting. LP bottles not empty. A 1/2” kinked flex on a high-BTU tank. Missing sediment trap on a recent swap. Utility red tag. A main that lights soft, yellow-tips, then drops is starving — it looks exactly like a bad thermopile.
• Required tools: None on the fittings. Manometer work is licensed (typically about 3.5–7 in. w.c. natural gas / 10–11 in. w.c. LP at the appliance — confirm the rating plate).

Do not crack the union to “see if you have gas.” Mercaptan in the room is leave, then the utility.

Step 5: When it is actually the gas valve

• What to look for: Pilot wrapped on the generator, millivolts staying above dropout with the main open, arrestor clear, draft pulling, supply open — and the main still dumps or never opens. Internal operator or a failed ECO in the control. Match gas type, millivolt vs electronic, FVIR.
• Required tools: On a licensed truck: manometer, leak-detection solution, combustion analyzer. Not a “universal” valve from a parts bin with no leak test.

When DIY Ends: Calling a Licensed Pro

Stop at gas odor, delayed-ignition bangs, spillage at the draft hood, a scorched burner door, millivolt numbers you cannot take, and any valve replacement. You may follow the jacket once, confirm the shutoff position, and look for lint at the arrestor from outside. You may not hold the knob in, jumper the thermopile, or loosen fittings. A licensed plumber will measure millivolts under load, manifold pressure, and only then swap the control — then leak-test every joint. A $12 sensor on a $200 valve you just contaminated is how this becomes a second visit.

Frequently Asked Questions

Q: Why does my gas water heater burner light then go out while the pilot stays on? A: The thermopile is sagging when the main operator opens, the valve’s main operator is failing, or a rollout/ECO/FVIR safety is dropping the main. A holding pilot already proved the thermocouple path.

Q: Can a dirty FVIR screen make the main burner drop out? A: Yes. A packed flame-arrestor starves the main more than the pilot. The main lights, smokes, and the valve or rollout kills it. Clean-out is a combustion-seal job on FVIR tanks.

Q: Should I replace the gas valve if the burner will not stay lit? A: Not first. Prove millivolts under load, draft, and the arrestor. Replace the valve only when those pass and the main still will not hold — and hire a licensed fitter to leak-test it.