Water heater pilot light keeps going out? Here's why

First, safety

If you smell gas, don't try to relight anything. Leave the house and call 911 and your gas company from outside. A. O. Smith's lighting guide says not to continue if you smell gas, and to turn the gas off and wait at least 10 minutes before relighting an extinguished pilot so any built-up gas can clear.

Always follow the lighting instructions on your heater's label. Models differ.

How the pilot stays lit

On a standing-pilot heater, the small pilot flame heats a thermocouple (or a thermopile on some models). That makes a tiny electric current that holds the gas valve's safety open. If the flame goes out, the current stops and the valve shuts off the gas. That's a safety feature, and it's why so many pilot problems trace back to that sensor.

The 7 usual causes

1. Bad or dirty thermocouple. If it's broken, A. O. Smith notes the safety valve gets no power and the pilot won't stay lit once you release the knob. Sometimes it's just dirty or bent out of the flame.
2. Drafts. An open garage door or window can be enough to blow the pilot out.
3. Dirty pilot assembly. Dust and lint can choke the pilot so the flame is small, yellow or weak and doesn't heat the thermocouple enough.
4. Not enough combustion air. Modern heaters have a safety system that won't let the pilot run if there's an airflow problem. Clutter around the base, a blocked air intake screen or a tight closet can trip it.
5. Gas pressure changes. The pilot is sensitive to pressure dips. If other gas appliances act up too, call your gas company.
6. Kinked or clogged gas tubing. A pinched pilot tube starves the flame.
7. Failing gas control valve or ignition system. If the thermocouple is good and the pilot still drops out, the valve or electronic ignition may be at fault. That's a job for a pro.

Pilot is on but there's no hot water

If the pilot burns steadily but the main burner never fires, the thermostat setting may be too low, the gas valve may not be opening, or the burner may be clogged. Turn the temperature dial up a notch and listen for the burner. If nothing happens, call for a repair.

What you can safely check

• Close nearby doors and windows and clear anything stored around the heater.
• Look at the flame through the viewing window. A steady blue flame that wraps the thermocouple tip is what you want.
• Relight once, following the label. If it goes out again within a day, stop relighting and get it looked at.

Replacing a thermocouple is a common, inexpensive repair. Gas valve, flammable vapor sensor and venting problems are not do-it-yourself work.