A water heater pilot that lights but goes out when you release the button almost always means the thermocouple is not sensing the flame: it is worn, loose, bent out of the flame, or the pilot flame is too weak from a dirty orifice. A pilot that goes out hours or days later points to drafts, a clogged flame arrestor, combustion air or venting problems, or a failing gas control.
- The pilot heats a thermocouple, which holds the gas safety valve open; lose the signal and the gas shuts off by design.
- Goes out when the button is released: thermocouple, its connection, or a weak pilot flame.
- Goes out later: drafts, a lint-clogged flame arrestor, restricted combustion air, backdraft, low gas pressure or a failing control.
- Relight only by following the label on the tank, and never if you smell gas or the unit has been under water.
- Power-vent water heaters have electronic ignition, not a standing pilot; they reset by cycling power.
01 /How does a water heater pilot light work?
A standing pilot is a small, continuous flame under the tank that lights the main burner whenever the thermostat calls for heat. Next to it sits a thermocouple, a metal probe that produces a tiny electrical voltage when heated. That voltage holds open a safety magnet inside the gas control. If the pilot goes out, the thermocouple cools within a minute or so, the magnet releases, and the control shuts off all gas, pilot included. That is why a pilot that goes out stays out.
Some controls use a thermopile, a bundle of thermocouples that produces more voltage and can power the whole control. The principle is the same. Power-vent water heaters are different: Natural Resources Canada notes that all power-vented water heaters use electronic ignition instead of a continuous pilot. If yours has a fan on top and a power cord, see power vent troubleshooting, no hot water and power vent in winter instead.
02 /Why does my pilot light go out when I release the button?
A pilot that lights while you hold the button but dies when you let go means the gas control is not receiving enough voltage from the thermocouple. The pilot itself is fine; the proof-of-flame signal is not.
| Cause | Clue | Fix |
|---|---|---|
| Button not held long enough | Released after a few seconds | Hold for the time on the label, commonly about a minute |
| Thermocouple worn out | Tank several years old; symptom came on gradually | Replace the thermocouple (or pilot assembly on sealed units) |
| Thermocouple not in the flame | Flame visibly misses the tip | Reposition or replace the pilot assembly |
| Loose thermocouple connection at the control | Intermittent; worse after the unit was bumped | Snug the connection per the manufacturer |
| Weak or yellow pilot flame | Small, lazy, yellow or lifting flame | Clean the pilot orifice; check gas pressure |
| Failing gas control magnet | New thermocouple did not help | Replace the gas control (technician) |
03 /Why does my water heater pilot keep going out later?
A pilot that stays lit after relighting but is out again hours or days later is being disturbed or starved, or its control is failing intermittently. Look for a pattern: does it go out when the furnace or dryer runs, on windy days, or after a long shower?
| Cause | Clue | What to do |
|---|---|---|
| Clogged flame arrestor or air intake (sealed-combustion tanks) | Lint, dust or pet hair around the base; laundry room location | Vacuum the intake area; a technician cleans the arrestor and resets any thermal cutoff |
| Drafts | Goes out on windy days or when a door or window nearby is open | Close the burner door properly; stop drafts at the tank |
| Backdraft or poor venting | Goes out when exhaust fans, dryer or furnace run; soot at the draft hood | Stop: have the venting and combustion air checked. See carbon monoxide and water heaters |
| Restricted combustion air | Tank closed into a small room; tight house | Technician to check air supply |
| Condensation dripping on the pilot | Goes out after large cold draws | Usually settles; persistent water needs checking |
| Low or fluctuating gas pressure | Other gas appliances misbehave too | Gas utility or technician |
| Thermocouple or gas control near failure | Intermittent, getting more frequent | Replace the failing part |
04 /How do I safely relight a water heater pilot light?
Follow the lighting instructions printed on your water heater; they are specific to its control. The general sequence on most standing-pilot controls looks like this.
- Read the label
Find the lighting instructions on the tank, usually near the gas control.
- Turn the control to OFF and wait
Wait the time the label specifies, commonly five minutes, so any gas can clear. Then check for a gas smell, including near the floor. If you smell gas, stop.
- Set the control to PILOT
Turn the knob to the PILOT position.
- Press and ignite
Press and hold the pilot button (or the knob) and press the igniter button repeatedly until you see the pilot through the sight glass.
- Keep holding
Hold the button for the time on the label, commonly about a minute, so the thermocouple heats.
- Release and check
Release slowly. The pilot should stay lit. If it goes out, wait and repeat once or twice at most.
- Turn on
Turn the knob to ON or to your temperature setting. The main burner should light.
If the igniter does not spark, if the pilot will not light at all, or if it goes out repeatedly, stop after a few attempts. Repeated relighting releases unburned gas each time and can mask a real fault. Newer sealed-combustion tanks may have locked out on a thermal cutoff that owners cannot reset; that needs a technician.
05 /What does a technician do for a pilot that won't stay lit?
A licensed gas technician tests the thermocouple or thermopile output with a meter, inspects the pilot flame and cleans the pilot orifice, checks the flame arrestor or air intake, measures gas pressure, and checks venting and combustion air. On sealed-combustion tanks, the pilot, thermocouple and igniter are often a single assembly behind a gasketed inner door, and the gasket must be renewed when the door is opened.
Who may do this work depends on your province. In Alberta, for example, gasfitting is a compulsory certification trade: work on natural gas and propane equipment is restricted to certified journeypersons and registered apprentices. Ontario's safety regulator advises that any fuel-fired appliance be installed, serviced and inspected by a registered contractor. The can I replace my own water heater guide covers the rules province by province.
A thermocouple replacement is commonly quoted around $150–$300 as a service call including the part; the part alone is inexpensive. A replacement gas control is a larger job, commonly several hundred dollars installed, which on an older tank is the point to compare with replacement.
Before paying for a gas control on a tank near the end of its range, run it through the Tank Lifespan Predictor and look at the replacement cost guide. You can request quotes for either.
06 /Should a water heater pilot light always be on?
Yes, on a standing-pilot water heater the pilot is meant to burn continuously, including when the burner is off and the tank is up to temperature. The VACATION setting on many controls keeps the pilot lit while holding the tank at a low temperature. The pilot uses a small but steady amount of gas, which is one reason Natural Resources Canada's guide points to electronic ignition as an efficiency feature.
If you turn a water heater fully off, for example for a long absence, you will relight it by following the label on return. The water heater maintenance schedule includes a quick monthly look at the pilot flame: steady and mostly blue is healthy; yellow, lifting or sooty is a reason to call.
FAQQuestions people ask
How long do you hold the pilot button on a water heater?
Follow your label, but commonly about a minute after the pilot lights, so the thermocouple heats enough to hold the safety valve open. If it still goes out after a full minute, the thermocouple or pilot flame is the likely problem.
Can a water heater pilot light go out by itself?
Yes. Drafts, a clogged flame arrestor, backdrafting, condensation, low gas pressure or a failing thermocouple can all put it out. Occasional outages after a strong draft may be harmless; repeated ones need diagnosis.
Why won't my pilot light light at all?
The gas may be off at the heater's valve or the meter, the igniter may not be sparking, air may be in the line after gas work, or a sealed-combustion tank may have tripped a thermal cutoff. Stop after a few attempts and call if it will not light.
Why does the pilot light but the burner won't come on?
The control may still be on PILOT or VACATION, the tank may already be at temperature, the thermopile may be weak, or the burner orifice may be blocked. Turn the knob to your setting and run some hot water; if the burner still does not light, call a technician.
Do power vent water heaters have pilot lights?
No. Power-vent water heaters use electronic ignition. If one stops heating, check power and the vent termination, and cycle the power to reset it following the label.
My water heater pilot went out after a flood. Can I relight it?
No. Gas water heater labels warn against using a unit if any part has been under water. Have a licensed technician inspect it; a submerged gas control is normally replaced.