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SECTION 4 - FAULT FINDING
4.5 ‘L1’ - FLOW TEMPERATURE OVERHEAT LOCKOUT
4.6 ‘L2’ - IGNITION LOCKOUT
If the boiler is restarted does the
boiler ignite for a short time and
then extinguish?
YES
Is the Gas Pressure available at
the Boiler Inlet (>35 mbar)?
Check the ignition / detection
electrode and associated
harness for: continuity, visual
condition and position (Refer
to Section 3.12). Check if the
condensate pipe is blocked.
Check flue is installed correctly.
Replace as necessary.
NO
Check gas supply and
rectify fault
NO
YES
Is 24Vdc supply available at the
Gas Valve?
YES
Check spark generator and
associated harness for: continuity
and visual condition. (Refer
to Section 3.13) Are these
functioning correctly?
YES
Check ignition / detection
electrode and associated harness
for: continuity, visual condition and
position. (Refer to Section 3.12)
Are these functioning correctly?
NO
Check siphon and condensate
drain pipework for blockage and
rectify if necessary. Boiler now
working OK?
Check wiring connection
from gas valve to PCB for
continuity. If the wiring is
OK then replace the PCB
NO
Replace Spark
Generator and harness
as necessary
NO
Replace ignition /
detection electrode and
associated harness as
necessary
NO
Replace Gas Valve
YES
Unplug gas valve.
Is resistance between outside pins
between 120k
Ω
(± 20)?
YES
Replace Gas Valve
NO
RESTART PROCEDURE: to restart boiler press the restart button.
Is the Boiler and CH System filled with anti-freeze/
inhibitor solution and all isolation and radiator valves
open?
YES
Fill and vent the system and open all
isolation valves, then restart boiler
Has the pump impellor seized? Check by engaging
with a screwdriver pushing inwards and then turning
clockwise through the hole in the centre of the pump
NO
Is the Flow/Return differential across the
boiler in excess of 30ºC
YES
NO
Replace the Pump,
and restart boiler
YES
RESTART PROCEDURE: to restart boiler press the
restart button.
Check the Return Thermistors
Check resistance using a suitable multimeter
connected across the thermistor’s terminal pins
At 25
o
C expect
9,700 - 10,300 Ohms
At 60
o
C expect
2,400 - 2,600 Ohms
At 85
o
C expect
1,000 - 1,100 Ohms
