9
Symptoms
Possible causes
Remedy
Burner will not start
Incorrect voltage selected
Red ‘mains on’ does not illuminate.
Overheat thermostat tripped.
Check outlet and inlets are not obstructed. Check
fan speed. If problem persists replace thermostat.
Red light illuminates.
External controls, thermostats, time switch etc.
Adjust controls.
not calling for heat.
Loose electrical connection.
Check all connections.
Fan seized or faulty motor.
Replace fan, recommission heater, checking gas
pressure settings.
Sequence controller relay failing to pull in and/
Check vacuum switch is satisfactory, replace
or hold in.
sequence controller.
Vacuum switch not returning to normal (switch
Replace vacuum switch.
off) position.
Fan starts but burner does not attempt ignition. Insufficient vacuum generated by fan.
Clean fan blades with soft bristle.
Combustion chamber cover permitting air
Examine condition of sealing gasket, tighten
leakage.
down lid securely.
Vacuum impulse line between combustion
Fix securely in place.
chamber and vacuum switch insecure
or defective.
Vacuum switch ‘pulls in’ but electronic sequence
Replace burner sequence controller unit but first
controller does not proceed to programme
check that the cause of failure is not a short on
ignition sequence.
output circuit, by measuring resistance between
pins 2 and 7 of burner control unit plug. A
reading of 10,000 ohms indicates short circuit on
gas valve burner indicator light or associated
wiring.
Burner proceeds to ignition stage (normally
No spark.
Check electrode for cracks – replace if necessary.
indicated by audible spark valve energised
Check high tension connections are secure.
and ‘burner on’ light illuminated) but burner
Check spark gap is 3.5 ± 0.5mm. If no high tension
does not light.
output from electronic controller, replace
controller.
Gas safety valve faulty or defective.
Replace solenoid operator section of gas valve.
Insufficient gas pressure.
Set burner pressure to that indicated on data
badge (see commissioning).
Burner lights but shuts down after a few
Inadequate flame signal. This can be verified
Replace electrode. Check connections to electrodes
seconds.
by connecting a sensitive micrometer in
and terminal 4 of electric sequence controller plug
series with the violet wire which passes through
Replace the electronic sequence controller.
the combustion chamber bulkhead. The correct
reading should be 5µA ± 1µA.
Flame unstable.
Check cleanliness of burner and set burner
pressure as indicated on data badge.
Inadequate gas supply. Observe burner
If gas pressure drops below that indicated on
gas pressure with all heaters operating.
the data badge, examine gas supply pipework
for excessive pressure loss.
Insufficient vacuum at combustion chamber
Clean fan blades with soft bristle brush.
causing vacuum switch to cut off.
Inspect tube internally and clean if necessary
(see servicing instructions).
Heater shuts down after operating for a period
Refer to above.
If problem persists, replace vacuum switch.
of time.
7 Fault finding
