38
British Gas 100 & 125 RD2 -
Installation & Servicing
FAULT FINDING
FAUL
T FINDING FAUL
T FINDING FAUL
T FINDING FAUL
T FINDING FAUL
T FINDING FAUL
T FINDING
*
Refer to Frame 36
Before attempting any electrical fault finding ALWAYS carry out
preliminary electrical system checks, i.e. earth continuity,
polarity and resistance to earth using a suitable meter.
Detailed instructions on the cleaning and adjustment or
replacement of faulty components are contained in the
'Servicing' section of this publication.
Check all
connections to
PCB are
correctly made
and secure.
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°C replace control 'stat.
If below 90°C replace overheat 'stat.
START
Check the mains supply to the
terminal block and that there is a
demand for heat. Expect 230 V
AC. Press the lockout reset switch.
NO
YES
NO
Is there a live supply on the overheat
'stat? Expect 230 V AC.
Is the hot surface igniter glowing?
YES
YES
YES
Change fan
YES
NO
Rectify bad connection
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 LED 4 is ON.
Is the fan turning ?
Check all connections to PCB are
correctly made and secure.
If no fault found change PCB.
Check pressure switch sensing
pipes for blockages, bad
connections and reversed
connection.
Is pressure difference at switch
greater than 0.9 mbar?
Change fan.
Is fault
corrected?
YES
NO
Change pressure
switch. Is fault
corrected?
Does the main burner light ?
NO
YES
YES
Does the hot
surface
igniter turn
off?
NO
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? Expect 230 V AC.
YES
NO
YES
NO
NO
Is there a supply on the fan
connector at PCB .
YES
YES
NO
NO
Is there a supply voltage
at the gas valve?
Expect 230 V AC.
Can the overheat 'stat
be reset when the
system is cold ?
NO
YES
NO
Replace board 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 are
correctly made and secure.
If no error found, replace PCB.
YES
NO
Has the fuse blown on PCB ?
Refer to Frame 34.
Is there a
supply at the
fan ? Expect
230 V AC.
Replace the overheat thermostat.
Does main burner
cross-light from pilot?
Is the main burner
injector clear?
Replace main gas
solenoid valve
NO
NO
NO
Change igniter. Does
igniter work?
Component
LED 3*
LED 4*
Application of power.
Flash > 1/sec in sync with LED 4
Flash > 1/sec in sync with LED 3
Control 'stat open circuit or
On.
On.
waiting for demand.
Fan start up.
Off.
Flash > 1/sec
Run.
Off.
On.
Pump over-run.
On
Off.
Lock-out.
Flash < 1/second.
Off.
Sensor Faults
Flash > 1/second.
Off.
Reverse polarity.
Flash > 1/sec alternately with LED 4.
Flash > 1/sec alternately with LED 3.
