the boiler in excess of 25
o
C ?
Can the overheat condition be reset by pressing the
boiler reset button when the system is cold ?
NO
74
L.......A........ (OVERHEAT ERROR)
Fill and vent the system and open all
isolation valves
water and all isolation valves open ?
NO
Replace overheat thermostat
75
L....8..... (FAN ERROR)
red and blue at the fan connector as
reset button is pressed?
Replace fan
NO
Replace harness
76
H.....1..... (FLOW THERMISTOR ERROR)
Is there continuity between the
PCB and the thermistor ?
Check resistance, using a suitable multimeter
connected across the thermistors 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
pipe and disconnect thermistor wires.
Are the thermistor values correct ?
Replace the thermistor
NO
NO
Replace PCB
Check and replace wiring as necessary
Replace PCB
across yellow and pink
at the fan connector?
Check wiring harness for continuity. Is there continuity?
NO
NO
Replace the system pump
Increase the pump setting.
Is differential now below 25
o
C ?
NO
Set CH control knob to maximum.
Over 90
o
C Check control thermistor
(Refer to Frame 52) .
Under 90
o
C Replace overheat ‘stat
NO
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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