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icos - Installation & Servicing
FAULT FINDING
FAULT FINDING FAULT FINDING FAULT FINDING FAULT FINDING FAULT FINDING
75
H......F........ (FLAME DETECTION - SHORT CIRCUIT ERROR)
Replace flame detection electrode
Is there continuity between the 2 terminal pins ?
Replace PCB.
NO
YES
76
H.....4...... (FLUE THERMISTOR ERROR)
Check wiring for continuity from the
PCB to the flue thermistor
Can the fault condition be reset by switching
off the mains supply to the boiler ?
Is the system filled and vented and all
isolation valves open ?
Is the pump operating correctly? Ensure
flow through system.
NO
Check resistance, using a suitable multimeter
connected across the thermistor 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
Are thermistor values correct ?
Replace PCB
Replace thermistor
Fill and vent the
system and open all
isolating valves
YES
Check resistance, using a suitable multimeter
connected across the flue thermistor 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
Are thermistor values correct ?
Inspect heat
exchanger for
blockage or damage
in the flueways.
Clean or replace as
necessary
Replace thermistor
NO
77
H......n........ (PHASE REVERSAL ERROR)
Check wiring to the boiler for
reversed live and neutral
YES
NO
YES
NO
Remove flame detection electrode terminal from PCB.
H9/L9 (HEAT EXCHANGER OVERHEAT)
Note.
With V9 Primary Control PCB, overheat LA/HA or H9/L9 when
reset will display 3 horizontal lines and will not attempt to refire
until the temperature in the heat exchanger drops below 50
o
C.