20
221899A
9 Fault Finding
Diagram 9.3
7424
Diagram 9.2
7315
FUSE
TYPE F4A
AIR PRESSURE SWITCH CONNECTIONS
FAN
EV1
EV2
SPARK
ELECTRODE
AIR
PRESSURE
SWITCH
SL
(N/O)
(C)
(N/C)
br
br
bk
p
r
gy
y
br
bk
KEY
bk BLACK
br BROWN
b BLUE
p
PURLPLE
r RED
y YELLOW
gy GREY
MAIN TERMINAL STRIP CONNECTIONS
PRINTED CIRCUIT BOARD CONNECTIONS
O/H
CUTOFF
b
b
b
N
b
Check for 230V ac
between N and common
contact on air
pressure switch.
Check for 230V ac
between N and normally
closed contact of air
pressure switch.
Is there 230V ac between
Ls and N
Ensure that any external controls are calling for heat and circuit water is cold. If overheat neon
lit - check water system for overheating, reset by turning temperature control knob off and on.
If neon 6 is lit flame failure has occured. Reset boiler by turning temperature control to off and then on.
Do not operate the boiler without combustion chamber front fitted.
Before carrying out fault finding, ensure that gas, electricity and water are available at the boiler.
Is neon 1 lit?
NO
Check power supply
Is neon 2 lit?
NO
YES
YES
Faulty thermistor.
Replace.
Disconnect the 2 way
thermistor plug from the PCB.
Check that there is a resistance
between 14k - 2.5kOhms.
Faulty PCB.
Replace.
Is neon 3 lit?
Faulty PCB.
Replace.
YES
NO
NO
YES
YES
Faulty air pressure
switch. Replace.
Does sparking take place
(Listen for spark discharge.)
?
Faulty PCB.
Replace.
Check for 230V ac
between N and brown
and between N and black,
3 way connector on PCB.
Faulty PCB.
Replace.
NO
NO
Check continuity of
gas valve harness.
Faulty gas valve.
Replace.
Faulty harness.
Replace.
NO
YES
NO
Is the fan turning?
YES
NO
Is there 230Vac
on fan?
Faulty
PCB.
Faulty
fan.
Does burner light?
YES
YES
YES
YES
NO
NO
Is neon 4 lit?
NO
YES
Appliance working
satisfactorily.
Is integrity of
electrode and
HT lead good?
Replace as
necessary
Faulty
PCB.
YES
NO
YES
NO
NO
