48
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
76
H.....4...... (DRY FIRE THERMISTOR ERROR)
Check wiring for continuity from the
PCB to the dry fire 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)
YES
NO
YES
NO
Remove flame detection electrode terminal from PCB.
H9/L9 (FLUE GAS OVERHEAT)
YES
Check wiring to the boiler for
reversed live and neutral
Foot Note: POLARITY CHECKS
Use a multimeter (set to measure 230 V AC or more), connecting the black lead to a reliable Earth point (not Neutral for this
particular test).
You should find 230 V on terminal L and zero (or a small reading) on terminal N.
N.B. Some meters may trip residual current devices during this test.
Note. With V9 Primary Control PCB, overheat LA/HA or
H9/L9 when reset will display 3 horizontal lines and will
not attempt to re-fire until the temperature in the heat
exchanger drops below 50
o
C.
202414-6.pmd 19/02/2008, 13:0848
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