Pilot light will not stay lit

On a standing-pilot gas tank, the pilot's job is to keep the gas valve open through a thermocouple or thermopile: the pilot flame heats the sensor, the sensor generates a small voltage, and that voltage holds the safety valve open. Release the control knob and the pilot dies when the sensor cannot produce enough voltage, which is why a pilot that will not stay lit usually means the sensor, its flame, or the valve.

The distinction matters for the fix: a thermocouple that fails slowly may hold for minutes then drop out, while a weak or misaligned pilot flame never heats the sensor properly in the first place. Both look identical from the shower: no hot water, pilot out.

The technician's checks run in order: the pilot flame must be steady and must envelop the sensor tip; the sensor's millivolt output must meet the control's requirement; the connections at the control must be clean and tight; and the control itself must hold the valve once the voltage is good. Bradford White's service manual documents the thermocouple and thermopile tests and the pilot assembly service procedures behind these checks.

A draught through the burner compartment, a dirty pilot orifice, or a gas-pressure problem can each starve or disturb the pilot flame and produce the same symptom, which is why the flame is inspected before parts are replaced.

Relighting a pilot that will not stay lit is the most repeated homeowner action in water-heater service, and it is harmless only if the cause is understood. If the pilot dies the instant the button is released, the cause is the sensing circuit and relighting will not help. If gas smell appears at any point, stop and treat it as a leak: leave and call FortisBC or 911.