IDEAL icos system HE15 Installation And Servicing page 57

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84 H.....4.... (DRY FIRE THERMISTOR ERROR)
Can the fault condition be reset by switching off
the mains supply to the boiler ?
Check wiring for continuity from the
PCB to the dry fire thermistor
Check resistance, using a suitable multimeter
connected across the thermistor terminal pins.
o
At 25 C expect 9,700 - 10,300
o
At 60 C expect 2,400 - 2,600
o
At 85 C expect 1,000 - 1,100
Are thermistor values correct ?
YES
Replace PCB
85 H......F.....
Remove flame detection electrode terminal from PCB
Is there continuity between the 2 terminal pins ?
Replace flame detection electrode
86 H......n.....
icos system -
Installation and Servicing
FAULT FINDING
NO
Ohms
Ohms
Ohms
NO
Replace thermistor
(FLAME DETECTION ERROR)
YES
(PHASE REVERSAL ERROR)
Check wiring to the boiler for
H9/L9 (HEAT EXCHANGER OVERHEAT)
Is the system filled and vented and all isolation
valves open, including TRV's & Bypass?
Check the pump is operating correctly in
Heating & DHW and check temp diffs across
YES
Check Flow stat is
fitted - making contact
with pipe
YES
Check resistance, using a suitable multimeter
connected across the dry fire thermistor
o
At 25 C expect
o
At 60 C expect
o
At 85 C expect
Are thermistor values correct ?
YES
Check that a permanently open
bypass circuit is available during
the pump over-run period after
boiler shutdown. This can be
provided by either an automatic
bypass valve or a heat leak radiator
(no TRV) of at least 10% of the
minimum boiler output.
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
NO
reversed live and neutral
Flow & Return.
NO
Fill and vent the
system and open all
isolating valves
terminal pins.
9,700 - 10,300 Ohms
2,400 - 2,600 Ohms
1,000 - 1,100 Ohms
NO
Replace
thermistor
Replace PCB
o
C.
57