Relight a Water Heater Pilot Light (and Fix One That Won't Stay Lit)
No hot water usually means the pilot light has gone out. Relighting it is a 10-minute job — and if it keeps dying, the thermocouple that senses the flame is a $12 part you can swap yourself.
What is actually broken
The pilot is a small standing flame that ignites the main burner. It goes out when a draft blows it out, when the pilot orifice gets dirty, or — most often when it won't stay lit — when the thermocouple wears out. The thermocouple is a safety device: it sits in the pilot flame, generates a tiny voltage, and holds the gas valve open only while a flame is actually present. A tired thermocouple can't hold the valve open, so the pilot dies the moment you let go of the control knob.
Safety first
- Smell gas (rotten eggs) at any point? Stop. Don't light anything, don't flip electrical switches — leave the house and call your gas utility from outside.
- After turning the gas control off, wait a full 10 minutes before relighting so any unburned gas clears the burner chamber.
- This guide covers standard atmospheric-vent tank heaters with a standing pilot. Sealed power-vent and tankless units are different — check your manual or call a pro.
The fix, step by step
1 Confirm it's the pilot
Peek through the sight glass or access panel at the bottom of the tank: no small blue flame means the pilot is out. Also confirm the gas control knob on top of the valve is set to ON, and check that another gas appliance (a stove burner) lights — if nothing in the house has gas, the problem is the supply, not the heater.
Tip: A puddle under the tank or rust streaks down its side is a different problem — a leaking tank can't be repaired. Stop here and price a replacement.
2 Turn it off and wait
Turn the gas control knob to OFF and wait 10 minutes. This pause isn't optional: it lets unburned gas dissipate from the burner chamber so the relight doesn't go whoosh.
Tip: Use the wait to vacuum dust and cobwebs from around the base and air intake screen — a starved, dirty burner is a common reason pilots die repeatedly.
3 Relight the pilot
Turn the knob to PILOT. Press and hold it down (this manually opens the gas path to the pilot), then click the piezo igniter button repeatedly until the pilot lights — watch through the sight glass. No igniter button? Use a long lighter or fireplace match through the access opening. Keep holding the knob down for a full 30–60 seconds after the flame catches.
Tip: Count the full 60 seconds. Letting go too early is the #1 reason people conclude the thermocouple is bad when it just hadn't warmed up yet.
4 Bring the burner back
Release the knob slowly — the pilot should stay lit. Turn the knob to ON and set the temperature dial to about 120°F (usually marked with a notch or 'hot' setting). The main burner should fire with a whoosh within a few seconds. Let it run a full heating cycle before drawing conclusions.
Tip: 120°F is the sweet spot: hot enough to discourage bacteria growth in the tank, low enough to prevent scalding and save energy.
5 If the pilot won't stay lit: replace the thermocouple
Pilot lights while you hold the knob but dies the second you release, every time? That's the classic thermocouple failure. Turn the gas control OFF, let everything cool, then unscrew the old thermocouple: a thin copper tube running from the control valve down to the pilot assembly, held by a small nut at the valve and a clip or nut at the burner. Install the new one in the same routing, snug (not forced), relight per steps 3–4, and test.
Tip: Take the old thermocouple with you to the store — they come in different lengths (12"–36"). Universal ones fit most heaters; match the length, and don't kink the copper tube on install.
Stop and call a pro if…
Call a licensed plumber or your gas utility if you smell gas at any point, if the new thermocouple doesn't cure it (that points at the gas control valve itself — a pro-level part), or if the tank leaks. Post the job through Find a Pro, or open the app and photograph the rating plate so a pro arrives with the right parts.
Your work, your responsibility
If you do this repair yourself: you attempt it entirely at your own risk. This guide is general information, not professional advice, and it can be wrong or incomplete. ClickTheFix is not responsible for injury to you or anyone else, or for damage to your property, that results from following — or misfollowing — this guide. Follow the safety warnings, use proper protective gear, follow the manufacturer's instructions and your local codes, and stop if any step is beyond your skill or comfort.
If a contractor does the work: any contractor you hire is an independent professional working under an agreement between you and them alone. ClickTheFix does not provide repair services, does not supervise or control their work, and does not guarantee or warranty it. ClickTheFix is not liable for a contractor's errors, omissions, poor workmanship, property damage, or injuries.