Component
Thermocouple and thermopile
Pilot-flame sensors that hold the gas valve open: a thermocouple drives the safety valve, and a thermopile generates more power to run millivolt controls. Either failing is the classic cause of a pilot that will not stay lit.
If you smell gas
- Stop what you are doing. Do not use phones, switches, matches or anything that can spark inside.
- Go outside and leave the door open behind you.
- Call the FortisBC 24-hour emergency line at 1-800-663-9911 or dial 911.
Only after that, call CANRO about the water heater. Official guidance: FortisBC gas leaks and odour.
How the pilot holds itself on
When you light a standing-pilot tank and hold the control in, the pilot flame heats a sensor in the flame. The sensor generates a small voltage, and that voltage holds a safety valve open once you release the knob. A thermocouple makes enough power for the valve; a thermopile, a stack of thermocouples, makes more and also powers millivolt electronic controls such as the ICON System's circuit.
The sensor only works when the pilot flame envelops its tip: a lazy flame, a draught, a dirty pilot orifice or a misaligned sensor all read as a failed sensor.
The symptom and the test
A pilot that dies the moment the knob is released is the sensor circuit's signature. The technician's test measures the sensor's millivolt output against the control's requirement with the pilot burning properly, then decides between the sensor, the pilot assembly and the control. Replacing the sensor without checking the flame is the classic repeated repair.
Frequently asked questions
What is the difference between a thermocouple and a thermopile?
A thermocouple drives a simple safety valve; a thermopile produces more voltage and also powers millivolt controls. The manual for the tank identifies which is fitted.
Why does my pilot stay lit for minutes, then die?
A sensor on the edge of its output can hold for a while and drop out as the flame or the part drifts; the millivolt test catches it where the symptom alone cannot.
Request a consultation
CANRO reviews your hot-water demand, equipment and installation constraints. Requests are confirmed by CANRO.
On-site service in Metro Vancouver, BC. Call to check availability.
Related
Sources and verification
- CANRO Heating & Cooling — About · Canadian source · accessed September 7, 2026
- Bradford White Defender Service Manual (thermocouple and thermopile tests) · 238-51542-00E · accessed September 7, 2026
Facts checked September 7, 2026. Last updated September 7, 2026. Technical reviewer: not yet assigned.