Description
As fitted to the Malaga Mk4 and Mk5 this sensor measures the temperature of the water and tells the main control board when it needs to be in heating mode or on standby.  The sensor consists of a thermistor potted into either an M5 or M6 bolt that screws into the casting of the tank and then plugs into CN2 of the main circuit board.
Failure of this sensor will stop the heater switching on in either Gas or Electric mode and so the heater will appear dead.
The correct operation of this sensor can be tested by measuring the resistance across the sensors two pins.  if operating correctly the resistance should be approx 11 – 13kOhms with the sensor at ambient or room temperature.  As the sensor warms up the resistance should drop steadily. At 3kOhms the sensor would be telling the control board the water has reached 70 degrees C.  So if your sensor is reading below that at ambient then the heater is not going to switch on.
A ‘quick’ test of the operation of the sensor on a ‘dead’ Malaga is with 12v present at the main control board, unplug the thermistor from CN2, if the switch panel now shows a fault light then chances are the sensor is bad.
All Malaga Mk4’s were fitted with M5 thermistors. Some time in 2018 the Malaga Mk5 changed from an M5 to an M6 bolt.  To confirm what bolt size you have then a 10mm spanner will fit the M6 bolt head and an 8mm spanner will fit the M5.
