Older furnaces and boilers use a standing pilot light to ignite the main burner. When it won't stay lit, the heat won't come on. Here are the usual reasons.
A worn thermocouple
The thermocouple senses the pilot flame and keeps the gas valve open. When it wears out, it shuts off gas even though the flame is fine. This is the most common cause and an inexpensive part to replace.
Dirty pilot tube or weak flame
A healthy pilot flame is steady and blue. A small, yellow or flickering flame often means a dirty pilot orifice that isn't heating the thermocouple enough.
Drafts and gas supply problems
Strong drafts, a blocked flue or a gas supply interruption can also put the pilot out. If you smell gas, leave the house and call your gas utility first.
Frequently Asked Questions
+Is it safe to relight a pilot light?
Following the instructions on your appliance label is generally safe. If it goes out again quickly, or you smell gas, stop and call for service.
+Should I upgrade from a standing pilot?
Modern furnaces use electronic ignition, which is more efficient and reliable. If your system is old enough to have a pilot, it may be time to compare options.
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