Pilot Light Is Lit but the Burner Won't Come On
On this page (5 sections)
The Short Answer: A lit pilot means the gas supply and the pilot safety are working. If the main burner never comes on, first make sure the gas knob is turned from PILOT to ON and the temperature is set above the current water temperature. If it still will not fire, the usual causes are a weak thermopile on electronic-thermostat controls, a tripped high-temperature limit, a clogged burner orifice, or a failed gas control.
Start with the settings
Most “no burner” calls with a lit pilot are settings:
- Gas knob still on PILOT. After lighting, the knob must be turned to ON. On PILOT, the main burner cannot open.
- Temperature on VACATION or very low. The burner lights only when the water is cooler than the setting.
- Tank already hot. If you have not used hot water, the burner has no reason to start. Run a hot tap for several minutes, then check.
If the settings are right
| Your heater | Most likely cause | Notes |
|---|---|---|
| Gas control with a status light (thermopile-powered, common on newer FVIR tanks) | Thermopile output too low to open the main valve, or a sensor or limit fault | Count the status-light flashes and check the chart on the heater’s label |
| Older control with a thermocouple and a dial (no status light) | Thermostat in the control failed, high-temperature limit tripped, or main valve failed | Some older controls have a reset; see the label |
| Any type, burner tries to light with a “whoomp,” or soot is present | Burner or orifice problem, or delayed ignition | See water heater made a loud bang |
| Burner lights then shuts off within a minute, pilot stays lit | Different symptom | See gas water heater burner won’t stay lit |
| Burner runs but water stays cool | Different symptom | See gas water heater burner on but no hot water |
A thermopile is a thicker flame sensor that produces enough electricity to power the gas control’s electronics and main valve. It can generate enough to keep the pilot lit while being too weak to open the main burner valve, which is why “pilot fine, burner dead” is a classic thermopile symptom on those controls.
What you can check safely
- Confirm the knob position and temperature setting as above.
- Watch the status light if your control has one and write down the flash pattern.
- Look through the sight glass at the pilot. It should be a steady blue flame wrapping the top of the sensor. A small or yellow pilot can mean a dirty pilot or a pilot tube restriction.
- Keep the air intake at the bottom of the heater clear of lint and dust.
- If the label describes a reset for your control, follow it once. If the problem returns, stop.
What the technician will check
The technician measures the thermopile’s output with the main valve calling for heat, checks the temperature sensor and the high-limit, inspects the burner orifice and burner for blockage, and confirms gas pressure at the control. If the thermopile is weak, it is replaced, often with the whole pilot assembly on FVIR tanks. If the thermopile and sensor test good and the main valve still does not open, the gas control is replaced. A high-limit trip is investigated for its cause, since it means the water got too hot.
Frequently Asked Questions
Q: Will a new thermocouple fix a burner that won’t light? A: Usually not. On thermocouple controls, a lit pilot that stays lit shows the thermocouple is doing its job. On thermopile controls, the thermopile (not a thermocouple) is the part to check. Installing the wrong type of sensor causes its own problems; see pilot won’t stay lit after replacing the thermocouple.
Q: The burner came on after I turned the temperature way up. Is that a fix? A: It means the control works but was satisfied, or the sensor is reading high. Turn it back to your normal setting; leaving it high increases scalding risk. If the burner will not run at a normal setting with cool water in the tank, have the temperature sensor 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.
- PG&E: recognizing and responding to a gas leak (opens in a new tab)Emergency actions for suspected fuel-gas leaks.
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