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classic HE - Installation & Servicing
FAULT FINDING
FAULT FINDING FAULT FINDING FAULT FINDING
Check all connections to PCB.
If no fault found, replace PCB
Reset the overheat 'stat. Set control
'stat to maximum. Allow the boiler to
reach temperature - if the overheat
'stat trips again, measure flow
temperature.
If above 90
o
C replace control 'stat.
If below 90
o
C replace overheat 'stat.
START
Is the mains on neon 'I3' illuminated?
YES
NO
YES
Is there a live supply on EITHER
terminal of overheat 'stat?
Is the ignition electrode sparking?
YES
NO
Check mains supply and fuses.
Check programmer and system
thermostats are all ON.
Check that boiler plug and socket
are OK and fully connected.
Check that the boiler thermostat is
set at maximum and the mains on/off
switch is ON. Is the fan turning ?
Replace the sensor
Check connections and leads to
pressure switch. If no fault found
change pressure switch.
Check all connections to PCB.
If no fault found change PCB.
Check pressure switch sensing
pipes for blockages, bad connections
and reversed connection.
Check S trap for blockage.
Is pressure difference at switch
greater than
0.9 mbar?
Change
fan
YES
NO
Change
pressure switch
Is the boiler casing
correctly fitted?
Does the pilot light ?
YES
NO
Does the spark
stop after the
pilot is lit?
Is there a gas
supply to the
boiler?
Is the pilot
injector blocked?
YES
Replace
gas valve
NO
Is there a supply on terminals
of main gas valve?
YES
NO
YES
NO
NO
Is there a supply on the fan
connector at PCB ('Molex'
marked 'FAN'?).
YES
YES
NO
NO
Check the
polarity of the
mains supply.
Check the
continuity of
the ignition
lead from
connector to
electrode.
Does the
spark now
cease when
gas is lit?
Ensure pilot and
main gas valve
leads are not
crossed over.
Is there a supply
voltage at pilot
gas valve?
Is there a live supply on the red
lead to the pressure switch?
NO
Is there a regular spark from
tube 'SG1' on the PCB?
Can the overheat 'stat
be reset when the
system is cold ?
NO
YES
NO
Replace fuse BUT, before
attempting to start boiler, check for
short between live and neutral,
also between live and earth, on all
items plugged into PCB
Check all connections to PCB.
If no error found, replace PCB.
Remove the sensor
(NTC) from the PCB.
Is the fan turning ?
YES
NO
NO
YES
Has the fuse blown on PCB ?
NO
NO
Is there a live supply on the
violet lead to pressure switch?
Is there a supply at the fan?
Replace the overheat thermostat
Does main burner
cross-light from pilot?
Is the main burner
injector clear?
Replace main gas
solenoid valve
Check gap at ignition electrode.
Check electrode and lead are
undamaged and not close to
earthed metalwork.
YES
YES
Change
fan
YES
NO
Rectify bad
connection
YESNO
YES
NO
YES
Check PCB by substitution
Is there a live supply on
BOTH terminals of limit stat?
YES
Change limit thermostat
NO
NO
Is there a live supply on BOTH
terminals of overheat 'stat?
YES
YES
If condensate pump kit fitted check
continuity of C-NC terminals
Check for condensate blockage
NO
Is there a live supply on BOTH
terminals of the flue protection stat
YES
Reset flue protection thermostat
YES
Change flue protection thermostat
NO
201850-6.pmd 21/02/2008, 12:5842