FIND FAULT
POSSIBLE CAUSES SOLUTION
Flame failure (lockout)
at low fire
Faulty low fire bypass valve
(high low burners only)
Low fire flame set too low
Check electrical supply to
valve
Check condition of the valve
if faulty, replace
Low fire flame set too low
Check the adjustment of the
gas control valve
Ensure gas is available at
burner
Too much air
Check and reset air at high and
low fire
Low fire air set too low
(modulating gas and air
burners only)
Check and adjust
Control circuit operating
due to
temperature ‘creep’
Check control circuit, over
temperature limits and low fire
settings
Flame sensor not detecting
Flame
Check flame sensor installation
and position
Main flame too long
Too much gas
Check main gas pressure and
reset
Check gas control valve and
reset
Check fuel type
Combustion air set too low
Check air dampers, linkages
and air filter (where fitted)
Fault Finding Guide
Comtherm Ltd
Installation & Maintenance Manual
Page 14
Burners, Heaters & Combustions Systems