Ultraviolet scanners see the UV light of a gas or oil flame, infrared scanners see flicker, flame rods use the flame's ability to conduct a small rectified current, and residential oil burners use a cadmium sulfide cell whose resistance drops under about 1,000 ohms in light. A weak or wandering flame signal is a common cause of lockouts, and techs read it in microamps or volts at the safeguard.
Flame signal's only 1.2 volts, pull the scanner and clean the lens, it's probably sooted up again.
A UV scanner that sees the spark can fool the safeguard, which is why spark rejection checks are part of a burner startup.
Also heard as
- scanner
- flame detector
- the eye
Related terms
Flame safeguard
The control that runs a burner's start sequence, watches the flame, and shuts the fuel off fast if the flame fails.
Pilot
A small flame that lights the main burner and is often used to prove ignition before main fuel flows.
Lockout
A safety shutdown that holds the burner off until someone presses a manual reset.
Nuisance trip
A safety shutdown or lockout caused by a faulty or marginal device, not by a real unsafe condition.