56
FAULT FINDING
F
AUL
T FINDING F
AUL
T FINDING F
AUL
T FINDING F
AUL
T FINDING F
AUL
T FINDING
isar + programmer -
Installation and Servicing
87 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
Are thermistor values correct ?
Replace PCB
Replace thermistor
Fill and vent the
system and open all
isolating valves
YES
Are thermistor values correct ?
Inspect heat
exchanger for
blockage or damage
in the flueways.
Clean or replace as
necessary
Replace thermistor
NO
89 H......n..... (PHASE REVERSAL ERROR)
Check wiring to the boiler for
reversed live and neutral
YES
NO
YES
NO
88 H......F..... (FLAME DETECTION ERROR)
Replace flame detection electrode
Is there continuity between the 2 terminal pins ?
NO
YES
Remove flame detection electrode terminal from PCB
Replace PCB
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
Check resistance using a suitable multimeter
connected across the dry fire 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
H9/L9
(HEAT EXCHANGER OVERHEAT)
202851-1new.pmd
17/11/2006, 07:41
56