Water Heater Pilot Light Won't Stay Lit
If a gas water heater pilot lights but goes out when you release the knob, the thermocouple (or thermopile) is the most common cause. It is a $10 to $30 part, and a plumber typically charges $150 to $300 to replace it. A dirty pilot tube, a draft or a failing gas control valve are the other usual causes.
Typical pro cost
$150 to $600
- Urgency
- Fix today
- DIY difficulty
- Medium
- Time to fix
- 30 minutes to 2 hours
- Prices
- US typical range
Last reviewed October 2026
Signs it's this problem
- No hot water and the pilot window is dark
- The pilot lights but goes out when you let go of the knob
- A weak, yellow or flickering pilot flame
- The pilot goes out every few days
- Clicking from the igniter with no flame
Common causes
Worn thermocouple
The thermocouple senses the pilot flame and keeps the gas valve open. When it wears out, the pilot shuts off as soon as you release the knob.
Dirty pilot tube or orifice
Dust and soot shrink the flame so it no longer heats the thermocouple properly.
Draft or backdraft
Wind down the vent or a nearby fan or door can blow the pilot out.
Bent thermocouple
If the tip is not sitting in the flame, it cannot stay hot enough.
Failing gas control valve
If a new thermocouple does not help, the valve on the front of the tank may be failing.
How to fix it, step by step
- 1
Read the lighting instructions on the tank label. Turn the gas control knob to OFF and wait 5 to 10 minutes for gas to clear.
- 2
Turn the knob to PILOT, hold it down and press the igniter (or use a long lighter) until the pilot lights.
- 3
Keep holding the knob for 30 to 60 seconds, then release. If the pilot stays lit, turn the knob to ON.
- 4
If it goes out when you release, the thermocouple is the likely cause. Check that its tip sits in the pilot flame.
- 5
A blue, steady flame should wrap the thermocouple tip. A small yellow flame means the pilot needs cleaning.
- 6
Replace the thermocouple if it still fails, or call a plumber if the gas valve is suspected.
Tools and materials
- Long lighter (if no igniter)
- Flashlight
- Adjustable wrench
- Universal thermocouple
Approximate DIY cost: $10 to $30
Call a pro when
- You smell gas at any time
- The pilot will not light at all
- A new thermocouple did not fix it
- The tank is leaking or more than 10 years old
Water Heater Pilot Light Won't Stay Lit cost
| Job | Typical cost |
|---|---|
| Thermocouple replacement | $150–$300 |
| Clean pilot assembly and burner | $100–$250 |
| Gas control valve replacement | $300–$600 |
| Plumber service call and diagnosis | $75–$200 |
| New gas tank water heater (50 gallon), installed | $1,600–$2,800 |
Ranges are typical US prices compiled by FixHomeCost. Prices vary by region, home and contractor, so compare 2–3 local quotes.
Common questions
Why does my pilot light go out when I let go of the button?
Almost always the thermocouple. It is not sensing the flame, so the gas valve closes when you release the knob.
How long does a thermocouple last?
Often 5 to 10 years. Soot and a weak flame shorten its life.
Can I replace a water heater thermocouple myself?
Many handy homeowners do. Turn off the gas at the control and the supply valve first. If you are not comfortable working near gas lines, hire a plumber.
Is it safe to keep relighting the pilot?
Relighting once or twice is fine. If it keeps going out, find the cause; repeated attempts with a faulty valve are not safe.
Related guides
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