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icos - Installation & Servicing
FAULT FINDING
FAULT FINDING FAULT FINDING FAULT FINDING FAULT FINDING FAULT FINDING
Does the pump setting give a differential
across 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 ?
YES
YES
NO
72
L.......A........ (OVERHEAT ERROR)
Fill and vent the system and open all
isolation valves
Is the boiler and CH system filled with
water and all isolation valves open ?
NO
Replace overheat thermostat
73
L....8..... (FAN ERROR)
Is nominal 330 V DC present across
red and blue at the fan connector as
reset button is pressed?
Replace fan
YES
NO
Replace harness
74
H.....1..... (FLOW THERMISTOR ERROR)
YES
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
Remove the boiler flow thermistor from the CH flow
pipe and disconnect thermistor wires.
Are the thermistor values correct ?
Replace the thermistor
NO
NO
YES
Replace PCB
Check and replace wiring as necessary
Replace PCB
YES
Is 14V DC present
across yellow and pink
at the fan connector?
Check wiring harness for continuity. Is there continuity?
NO
YES
NO
Replace the system pump
Increase the pump setting.
Is differential now below 25
o
C ?
YES
OK
NO
YES
Set CH control knob to maximum.
If the overheat trips again measure the flow temp:
Over 90
o
C Check control thermistor
(Refer to Frame 71) .
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 refire
until the temperature in the heat exchanger drops below 50
o
C.