50
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 ?
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
YES
NO
77
H......n........ (PHASE REVERSAL ERROR)
Check wiring to the boiler for
reversed live and neutral
Remove flame detection electrode terminal from PCB.
H9/L9 (HEAT EXCHANGER OVERHEAT)
Is the system filled and vented and all isolation
valves open, including TRV's & Bypass?
Check the pump is operating correctly in
Heating & DHW and check temp diffs across
Flow & Return.
YES NO
Fill and vent the
system and open all
isolating valves
Are thermistor values correct ?
Check that a permanently open
bypass circuit is available during
the pump over-run period after
boiler shutdown. This can be
provided by either an automatic
bypass valve or a heat leak radiator
(no TRV) of at least 10% of the
minimum boiler output.
Replace
thermistor
YES
NO
Check resistance, using a suitable multimeter
connected across the dry fire 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
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.
Check Flow stat is
fitted - making contact
with pipe
YES
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