56
icos system - Installation and Servicing
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 ?
Replace the system pump
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 83) .
Under 90
o
C Replace overheat 'stat
YES
YES
Check that the pump is rotating freely.
Is differential now below 25
o
C ?
NO
NO
81
L......A..... (OVERHEAT ERROR)
Fill and vent the system and open all
isolation valves
YES
Is the boiler and CH system filled with
water and all isolation valves open ?
OK
NO
YES
NO
Replace overheat thermostat
82
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
83
H.....1..... (CONTROL THERMISTOR ERROR)
YES
Is there continuity between the
PCB and the thermistor?
Remove the boiler control thermistor from
either the CH flow/return 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
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
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.
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