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©G Hendra Nov 18
50
Using a meter, measure the resistance of the sensor, to do this un plug the sensor from the
PCB, set your meter to the ohms or
Ω
setting, Measure resistance across the sensor and
compare the reading from the meter to the tables below.
All sensors change resistance with temperature, it’s important to check the sensor reads the
correct value for the temperature it is measuring.
Fault Code, Plug number, Sensor
E251
CN43 CN43, white plug in top right-hand corner of the PCB,
blue sensor for compressor discharge pipe. 2
nd
from top on the plug
(wire 3 and 4). Number 5 in the K4 menu
E320
CN43, white plug, blue sensor for OLP compressor casing
sensor (Probe looks different to the usual, this one is more of a flat
disc). The 1
st
sensor of the plug (Wire 1 and 2). Number 6 in the K4
menu
E904:
Indoor unit MIM PCB, yellow plug, blue sensor for hot water
cylinder. Only used if field setting value 3011 is set to 1. This
temperature is read at the indoor controller, using the view button.
E901
CN44 yellow plug, blue sensor for outdoor unit heat exchanger (inlet/Return). Top
sensor of this plug (Wire 1 and 2). Number 7 in the K4 menu.
E902
CN44 yellow plug, blue sensor for outdoor unit heat exchanger (Flow/outlet). Middle
sensor of this plug (Wire 3 and 4). This sensor can be viewed from the indoor unit, using the
view button.
.
E221
CN43, white plug, red sensor for ambient air (Back of the unit).
The bottom sensor of the plug (Wire 7 and 8). Number 4 in the K4
menu
E231
CN43, white plug, red sensor for outdoor unit evaporator coil.
2
nd
from bottom of the plug (Wire 5 and 6). This sensor cannot be
viewed in the K4 menu
E906
CN44 yellow plug, red sensor for refrigerant temperature under
the expansion valve. Bottom sensor of this plug (Wire 5 and 6). This
sensor cannot be viewed from the K4 Menu
E903
red sensor for backup boiler in the control box only active if field
setting 4021 is set to 1, can be viewed in indoor unit, in test mode.
E653
sensor in the remote controller red no resistance available sensor can’t be changed
If your sensor reads well within the range that you would expect for the temperature it’s
measuring, look at the PCB for cracked soldered joints and loose connections, you’ll probably
need a new PCB.