Pilot Goes Out When You Turn the Temperature Dial
On this page (5 sections)
The Short Answer: If the pilot stays lit while held on PILOT but goes out as soon as you turn the knob to ON or raise the temperature, the pilot’s flame sensor (thermocouple or thermopile) is usually not producing enough signal to hold the gas valve open once the main burner draws gas. Other causes are a gas supply that drops when the main burner opens, a weak or dirty pilot flame, or a worn gas control.
Which knob did you turn?
Standing-pilot heaters often have two controls that people call “the dial”: a gas knob marked OFF / PILOT / ON, and a temperature dial. Some combine them. Note which one you moved and what went out.
| What happened | Likely cause |
|---|---|
| Pilot goes out the moment you release the gas knob or turn it from PILOT to ON | Thermocouple or thermopile not heating enough, a loose sensor connection, or a weak gas-control magnet |
| Pilot stays on at ON, then goes out when you raise the temperature and the main burner lights | Gas pressure dropping when the main opens, a pilot flame disturbed by the main burner, or a weak thermopile on electronic-thermostat controls |
| Main burner lights, then shuts off, but the pilot stays lit | A different problem; see gas water heater burner won’t stay lit |
| Pilot will not stay lit even on PILOT | See why a gas water heater won’t stay lit |
Why turning the knob matters
While you hold the knob on PILOT, you are holding the pilot gas open by hand. When you release it, the valve stays open only if the flame sensor is producing enough electricity to energize the safety magnet. A sensor that is worn, slightly out of the flame, or connected loosely can be just good enough during lighting and fail moments later.
When the main burner opens, it draws much more gas. If the supply line is undersized, a propane tank is low or cold, or the regulator is weak, pressure at the pilot can dip and shrink the flame. On some controls powered by a thermopile, the main burner’s demand also pulls the voltage down; if it drops below what the control needs, the pilot and burner shut off. In cold weather propane pressure drops further; see pilot light goes out in cold weather.
What you can check safely
- Follow the lighting label exactly, including how long to hold the knob after the pilot lights. Releasing too early is a common cause.
- Look at the pilot flame through the sight glass. It should be a steady blue flame wrapping the tip of the sensor. A small, yellow, or wavering flame points to a dirty pilot or low gas.
- Check other gas appliances. If their flames dip when the water heater’s burner starts, suspect supply pressure.
- On propane, check the tank level.
- Keep the air openings at the base clear of lint and storage.
Do not keep relighting and cycling the knob. Two or three attempts following the label is enough before calling a technician.
What the technician will check
A technician measures the thermocouple or thermopile output with the pilot lit and again with the main burner running, cleans or replaces the pilot assembly, and checks supply pressure while the main burner fires. If the sensor output is good and the pilot still drops out, the gas control is usually replaced. On FVIR tanks the pilot and sensor sit inside a sealed chamber, so they are often replaced as one assembly; replacing a pilot assembly explains that repair.
Frequently Asked Questions
Q: Is a new thermocouple always the fix? A: It is the most common fix on thermocouple heaters, but not always. If a new thermocouple does not solve it, the gas control’s magnet or a supply pressure problem is next; see pilot won’t stay lit after replacing the thermocouple.
Q: Can I leave the knob on PILOT to keep it lit? A: The pilot may stay lit, but the main burner will not run on PILOT, so you will not get hot water. It also does not fix the underlying fault.
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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