A pilot light that lights but will not stay lit almost always comes down to one of three things: a worn thermocouple no longer holding the gas valve open, a draft blowing the flame out, or a dirty pilot assembly restricting gas flow to the flame. These same three causes apply across furnaces, water heaters and most other standing-pilot gas appliances.
If you ever smell gas, do not attempt to light a pilot — leave the area, do not operate any switches, and contact your gas utility or a technician immediately. The checks below assume no gas smell and are limited to observation; actual pilot assembly, thermocouple and gas valve repairs should be handled by a qualified technician.
How a pilot light stays lit
A small metal sensor called a thermocouple sits in the pilot flame. As long as the flame heats it, the thermocouple generates a tiny electrical current that holds the gas valve open. If the flame goes out for any reason, the thermocouple cools within seconds and the valve closes automatically — a safety feature, not a fault, that stops gas flowing without a flame to burn it.
Common causes
| Cause | How likely | What to look for |
|---|---|---|
| Worn or misaligned thermocouple | Very common | Pilot lights fine but goes out within seconds to a minute of releasing the control knob |
| Draft blowing out the flame | Common | Appliance near a door, window, or vent with noticeable airflow |
| Dirty or clogged pilot orifice | Common | Flame looks small, weak, or an unusual colour rather than a steady blue |
| Faulty gas control valve | Occasional | Thermocouple tests fine but the pilot still will not hold |
| Low gas pressure | Less common | Other gas appliances also showing weak flames |
How to check it
- Follow the manufacturer’s relighting instructions exactly
Every appliance has a specific procedure, usually printed on a label near the pilot assembly. Follow it precisely, including how long to hold the control knob in before releasing it.
- Time how long the flame lasts
A pilot that goes out the instant you release the control knob points strongly toward the thermocouple — it needs a certain amount of time being heated by the flame before it can hold the valve open on its own.
- Check for drafts
Look at the appliance’s surroundings for a nearby door, window, or vent that could be blowing across the pilot flame.
- Look at the flame colour and size
A healthy pilot flame is a steady blue, roughly the size specified in the manual. A small, flickering, yellow or orange flame suggests a dirty or partially blocked orifice.
When to call a technician
Cleaning a pilot orifice and replacing a thermocouple are common, generally inexpensive repairs, but they involve working directly with a gas appliance’s burner assembly. Have a qualified technician handle the actual part replacement rather than attempting it yourself unless you have specific experience with gas appliances.
Stop and call a qualified appliance technician or electrician if you find scorched or melted wiring, smell burning, see water that has reached electrical components, or if the fault returns immediately after a repair. Never bypass a safety device — thermal fuses, door interlocks and flood switches fail for a reason, and defeating one converts a broken appliance into a fire or flood risk.
