Don't blame the thermocouple until you've checked the draft

title: “Don’t blame the thermocouple until you’ve checked the draft” type=.report. source_topic: “Gas heater pilot problems”

A pilot that keeps going out is often the thermocouple, but a draft problem in the vent stack can absolutely cause it too.

The thermocouple is the safety gadget that senses the pilot flame and keeps the gas valve open. If it’s bad or positioned wrong, it shuts the gas off — that’s the classic suspect. But the pilot flame also needs stable airflow to burn. If the vent stack is blocked, or the chimney is creating a backdraft, cold air can push down and blow the pilot out every time it starts.

You can’t always see it, but the clues are there. If the pilot stays lit right after you relight it, then dies a few minutes later, and you notice a draft around the heater or a smell of exhaust, suspect a venting