How a Dishwasher NTC thermistor Sensor works & how to test it

by / Sunday, 14 December 2014 / Published in Dishwasher




 
The temperature is controlled by the PCB by means of a NTC thermistor temperature sensor incorporated in the heating element when you test it the Resistance drops as the temperature rises.




What is an NTC Sensor?

NTC sensor

Dishwasher NTC thermistor Sensor

 
A thermistor is essentially a resistor that changes its electrical resistance at varying temperatures. The name is derived from a mix of thermal and resistor. They are used in Dishwasher because their electrical resistance at various temperatures is known, it’s easy for the Dishwasher to monitor a thermistor and detect when certain temperatures are reached.

Check all connections first to the Dishwasher sensor and to the board they may have come loose, you are sometimes unlikely to see anything physically wrong but there might be a bad connection. Diagnosis is done by measuring the resistance with a continuity (or multi) meter. We can’t give readings for all thermistors because they vary, see my picture for an example, but you should be able to get a reading across both terminals. If it’s completely open circuit it’s likely to be faulty.

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7 Responses to “How a Dishwasher NTC thermistor Sensor works & how to test it”

  1. Sergey says : Reply

    Thank you, it is helpfull

  2. jens says : Reply

    Hallo, i need your help, i have a ariston ll64 dishwasher and i need to know where is the termistor ntc position, thanks for your answer and help!

  3. John says : Reply

    I have a Indesit dishwasher Model IDL605.It has had a start up problem Number 2 light comes on, you can here the pump draining then water entering, then it stops and number 1 and 3 light starts flashing and nothing happens, You can turn off power leave for a while then start up, and it goes through same motions. I have replaces pressure switch, have pulled pump out and no restrictions. Have looked at main board cant see any burn marks and all connections are tight. If any ideas I would appreciate Regards
    John Emms.

  4. Karen Lee Rose says : Reply

    How can I increase the kitchenaid dishwasher temperature during the drying cycle so that dishes will dry?

  5. Coen Burger says : Reply

    I have a Whirlpool dishwasher Model ADP4108/1, It has a water leak problem and it did not switched off. It continued to refill the unit with clean water, pump the water out and repeat the cycle. I repaired the water leak and tested the machine again. It filled the machine with about 5lit of water and then emptied the machine, that carried on until I switch the machine off. While testing the machine I noted that the indicator lamp flashes 9 times during the duration of the testing cycle. I suspected that it could be the PCB as the unit previously has been repaired by a Technician, and some of the contacts were bridged out. I therefore replaced it. When I retest the machine the indicator lamp flashes ones and nothing further happens. This indicates that the thermistor sensor could be faulty. Testing proofs no fault. You can turn off power leave for a while then startup, and it goes through same motions. Could the contacts be damaged inside the sensor I would appreciate any assistance. Where can I find spares for this machine in South Africa?.
    Regards

  6. Patrick Redig says : Reply

    Dishwasher stops after 21 minutes on repated trials just as the main wash cycle is starting, however, once in a great while it does continue through a complete wash cycle. Have gone through all connectors and plugs on circuit board – cleaned them and applied Deoxy before plugging back together. Also pulled the board and examined solder joints and traces under a microscope – no problems found. Problem persisted after reassembly. I’m thinking the problem has been isolated to the thermister. I measured resistance between P-2 (yellow with black stripe wire on the circuit board and neutral at room temp and got 56 ohms; when the machine quit after 22 minutes, the resistance was at 16 – 18 ohms instead of 12 – 13 – would this be sufficient to cause it to fail? Also, I cranked up the water heater so the incoming water was at 165 F which should have been more than enough to drive the resistance in the thermister down.

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