Gas Water Heater Burner Won't Stay Lit
On this page (6 sections)
The Short Answer: When the main burner lights and then goes out, the heater is either starved of something it needs (gas, combustion air, or electrical power from the pilot) or a safety device is shutting it down. On tanks with an electronic gas control and status light, a weak thermopile is a common cause. On any tank, a clogged air intake screen, poor venting, or low gas supply can also do it.
Which kind of control do you have?
How the main burner is held open depends on the gas control:
- Older standard controls use a thermocouple at the pilot. If the pilot stays lit, the thermocouple is doing its job, and a main burner that won’t stay on points elsewhere.
- Electronic controls with a status light (Honeywell/Resideo, White-Rodgers and similar) are powered by a thermopile, a larger sensor that the pilot heats to generate a small voltage. If that voltage is too low, the pilot can stay lit while the main valve won’t open or won’t stay open. On the Honeywell control in Bradford White’s service manual (opens in a new tab), two flashes with a three-second pause means low thermopile voltage with the main valve off. Check the label on your control, since codes differ between control makers and versions.
Common causes
| What you see | Likely cause | Urgency |
|---|---|---|
| Pilot steady, main lights briefly and goes out, status light flashing | Weak thermopile or a dirty or weak pilot flame | Service |
| Main flame lazy or yellow, then goes out; lint around the bottom of the heater | Clogged flame-arrestor or air intake screen on a flammable-vapor-resistant tank | Stop using it; service |
| Goes out when a dryer, range hood, or bath fan runs | Not enough combustion air, or exhaust spilling | Stop using it; service |
| Both pilot and main go out, sometimes with scorch marks at the burner door | Thermal (rollout) switch opening | Stop; see thermal switch keeps tripping |
| Soft, small flame that dies, other gas appliances also weak | Low gas supply or an empty propane tank | Check supply |
| Water dripping onto the burner | Condensation or a leak | Stop; see gas water heater dripping on burner |
What you can check safely
- Gas supply. The shutoff on the gas line should be parallel to the pipe. Check that other gas appliances work, and on propane, that the tank isn’t empty.
- The status light. Count flashes and match them to the label on the heater.
- Around the base of the heater. Most standard gas tanks built since about 2003 are flammable-vapor ignition resistant (FVIR) and draw air through a screen near the bottom. Keep the area clear of lint, dust, stored items, and anything flammable. Don’t take the burner area apart to clean it; that is technician work because the combustion chamber is sealed.
- The room. A heater in a small closet needs the air openings the installer provided. A louvered door that was replaced with a solid one can starve it.
- Relight once according to the label if the pilot also went out. If the problem returns, stop.
What the technician will check
A technician measures the thermopile or thermocouple output with the burner running, inspects and cleans the pilot assembly, checks the flame arrestor and combustion air openings, and measures gas pressure against the rating plate. They test for exhaust spillage at the draft hood with nearby fans running. Only after those checks pass would they replace the gas control.
Repair or replace
A thermopile, pilot assembly, or thermal switch is a moderate repair. Cleaning a clogged air screen is a service call. A gas control valve costs more but is still a repair on a sound tank. A tank with water leaking onto the burner needs replacement.
Frequently Asked Questions
Q: The pilot stays lit, so is the thermocouple fine? A: On a standard thermocouple control, generally yes. On a thermopile-powered electronic control, the pilot can stay lit even though the thermopile isn’t producing enough power to run the main valve.
Q: Why does it go out only when the dryer runs? A: A clothes dryer, range hood, or bath fan can pull air out of the house faster than it is replaced, drawing exhaust back down the water heater vent. That is a safety problem; stop using the heater and have the venting and combustion air checked.
Manuals and supporting references
These links distinguish general safety information from model-specific documentation. A manual directory helps you locate your unit’s instructions; it does not establish that every model uses the same parts, codes, or test values.
- Bradford White: service manual 238-51542-00A (Honeywell gas control troubleshooting chart) (opens in a new tab)Bradford White FVIR gas models covered by that manual with a Honeywell gas control; other controls use their own charts.
- PG&E: recognizing and responding to a gas leak (opens in a new tab)Emergency actions for suspected fuel-gas leaks.
- CPSC: carbon monoxide fact sheet (opens in a new tab)Carbon monoxide hazards and emergency response.
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