77
H......F........ (FLAME DETECTION - SHORT CIRCUIT ERROR)
Is there continuity between the 2 terminal pins ?
Replace PCB.
NO
78 H.....4...... (DRY FIRE THERMISTOR ERROR)
Check wiring for continuity from the PCB
Can the fault condition be reset by switching off
the mains supply to the boiler ?
valves open ?
through system.
NO
Check resistance, using a suitable multimeter
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
Replace PCB
thermistor
Fill and vent the
system and open all
isolating valves
Check resistance, using a suitable multimeter
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
Clean or replace as
necessary
Replace thermistor
NO
79
H......n........ (PHASE REVERSAL ERROR)
NO
NO
H9/L9 (FLUE GAS OVERHEAT)
Check wiring to the boiler for
reversed live and neutral
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-re until the temperature in the heat
exchanger drops below 50
o
C.
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