52
FAULT FINDING
F
A
U
L
T
F
IN
D
IN
G
F
A
U
L
T
F
IN
D
IN
G
F
A
U
L
T
F
IN
D
IN
G
F
A
U
L
T
F
IN
D
IN
G
F
A
U
L
T
F
IN
D
IN
G
excel HE -
Installation and Servicing
84 ERROR CODE 5 - CH THERMISTOR FAULT
Unplug thermistor
connector. Is resistance
approx. 10K OHMS at
25
o
C?
Re-connect and measure
voltage across thermistor.
Is it 3.75V DC nominal?
YES
NO
NO
NO
YES
Replace PCB
Fit and re-test
Drain waterset and replace
thermistor
Is PCB connector fitted
correctly?
YES
Is harness continuity OK?
NO
YES
Replace PCB
Replace harness
85 ERROR CODE 6 - DHW THERMISTOR FAULT
Unplug thermistor
connector. Is resistance
approx. 10K OHMS at 25
o
C?
Re-connect and measure
voltage across thermistor.
Is it 3.75V DC nominal?
YES
NO
NO
NO
YES
Replace PCB
Fit and re-test
Drain waterset and replace
thermistor
Is PCB connector fitted
correctly?
YES
Is harness continuity OK?
NO
YES
Replace PCB
Replace harness