Water heater pilot light won't stay lit: what is wrong
If the pilot lights while you hold the knob down and dies when you let go, the heater is shutting the gas off on purpose. Something is telling it the flame is not there, or that it is not safe to run.
Safety first
If you smell gas, do not relight anything. Leave the house and call Southwest Gas from outside. If you do not smell gas, follow only the relight steps printed on the heater's own label.
The usual causes, most common first
- Worn thermocouple (older standing-pilot heaters). The thermocouple is a small metal probe that sits in the pilot flame and produces a tiny current that holds the gas valve open. When it wears out, the valve closes as soon as you release the knob. Replacing it is a routine, low-cost repair for a plumber.
- Dirty or loose pilot assembly. Soot or debris in the pilot tube can leave a weak or yellow flame that does not heat the thermocouple properly. A weak flame can also come from a partly blocked pilot orifice.
- Thermocouple not sitting in the flame. If the probe has been bumped or bent, the flame no longer touches the tip.
- Failing gas control valve. If the thermocouple is new and the pilot still drops out, the valve itself may be the fault. On many heaters this means a replacement of the valve assembly, and at that point the age of the tank matters. See signs your water heater needs replacing.
- Drafts or poor combustion air. Garage heaters can be hit by wind through the door, or have lint and dust built up around the burner area. A blocked flue can also trip safety devices. Do not clear venting yourself.
- Newer heaters without a standing pilot. Many current models use electronic ignition and a flame sensor. A dirty sensor or an error code is the likely cause. The code chart is on the label or in the manual; write the code down before you call.
What you can safely check
- Confirm other gas appliances work, so you know the gas supply is on.
- Look at the flame through the viewing window if the heater has one. A steady blue flame is normal. A yellow, lazy or flickering flame points to soot, a blockage or poor air.
- Check the thermostat dial is not set to OFF or VACATION.
- Note the heater's age from the serial number label. Repeated pilot trouble on a heater near the end of its life is a good reason to price a replacement rather than keep repairing it.
What to leave to a licensed plumber
Anything involving the gas valve, the flue, gas piping or burner removal. Gas work in Clark County is not a DIY job, and a replacement still needs a permit; see water heater permits in the valley. For the whole checklist when there is no hot water at all, see no hot water: what to check first.
Hard water makes this worse
Las Vegas Valley water is very hard, and sediment builds up in the bottom of a gas tank where the burner sits. That makes the burner run longer and can leave scale and soot around the burner area. See hard water and your water heater.
Common questions
Why does my pilot light go out when I release the knob?
The safety system is not sensing a flame. On older heaters the usual cause is a worn thermocouple. On newer ones it is often a dirty flame sensor or an error that the display or status light will show.
Is it safe to keep relighting the pilot?
Not if it keeps going out. A pilot that will not stay lit means a safety device is doing its job. Get it diagnosed instead of repeatedly relighting it, and never relight if you smell gas.
Should I repair or replace?
A thermocouple is a small repair. If the gas control valve has failed, or the tank is near the end of its life or leaking, replacement is worth pricing.