How to test and replace the heater, thermostats, Ntc sensor

by / Tuesday, 13 January 2015 / Published in Heating Systems, Tumble Dryers

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If your tumble dryer is not heating and laundry comes out cold and wet you generally need to call an engineer, but there are a few things you can check. There is a good chance that it is a fault with the heater system. When your tumble dryer is not heating it is either a faulty heating element, or a faulty stat or TOC. (TOC is an acronym for thermal overload cut-out and it’s essentially a heat activated fuse). The Ntc sensors can also be faulty other common causes are faulty connections, and float switch or condenser sensor faults in condenser dryers.

Theromastats, TOC’s and Ntc sensors on 6th sense Tumble Dryer Whirlpool, Bauknecht, Laden & Maytag.

6th sense Thermostats, TOC’s and Ntc sensors sometimes all look the same. Sometimes they look virtually identical on most common tumble dryers. They tend to be small, round about 1 cm wide with two wires connected either side. On Theromastats & TOC’s Power flows through them to the heating element (or on the element’s neutral return) until a heat sensitive bi-metal strip inside bends under a specific heat temperature, and breaks the connection inside.

 

With Ntc sensors the temperature is controlled by the PCB by means of a NTC temperature sensor, This sensor consists of a resistor contained in a metallic capsule. Its resistance decreases as the temperature increases. The electronic circuit reads the resistance (which varies with the temperature inside the dryer); when this resistance falls below a certain value, the heater unit is switched off. As the air cools, the Resistance increases; when it reaches a given value, the electronic circuit re-connects the heater unit to the power supply. This occurs each time the temperature inside the dryer exceeds a given value, which varies according to the drying cycle that has been selected. All sensors have given values and need to be checked accordingly. See the workshop manual below for the correct values on this 6th sense Whirlpool Tumble Dryer and some models of Bauknecht, Laden & Maytag.

 

The heater is easily checked by doing a continuity test across the two sides of the circuit see video for this.

Pictures of the Heating system on Whirlpool, Bauknecht, Laden & Maytag Tumble Dryers.

 

 

heater, thermostats, ntc sensors 2

Terminal block Tumble Dryer Whirlpool, Bauknecht, Laden & Maytag

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heater, thermostats, ntc sensors Tumble Dryer Whirlpool, Bauknecht, Laden & Maytag.

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The workshop manual

I'm sorry this in mostly in italian as we have not found english version




9 Responses to “How to test and replace the heater, thermostats, Ntc sensor”

  1. Igor says : Reply

    Hello to all. I have one problem with Whirlpool AWZ 8665 dryer. The programator switch-off (I hear in programmator some click(s)…) the heating unit after app. 10 sec and no switch-on again until dryer is switched off. Then by new start of dryer the same procedure again…
    I checked NTC and is o.k., also other themperature switches and heating unit are o.k..

    What can cause such dryer work? Thanks in advance for your help and suggestions!

  2. John says : Reply

    Hi have change the heater on my whirlpool Awz 7913 as everything was working ecept l had no heat ,the new heater has not made any difference .would you advise me to look at the ntc now ????

  3. Mick says : Reply

    After having the fault code ‘F04’ I have followed the instructions to makes sure all the filters and water collector are clear, but the fault persisted. So followed the instructions to check the Thermostat, NTC sensors (both of them) and also the Heater. Thermostat and Sensors seem OK but can’t be sure about the heater. There seems to be continuity between the fist contact and the second, and also between the first and third. there seems to be no connection between the other connecters and any others. I can’t tell from your video which contacts should have some continuity so can’t be sure that the neater is working OK nor not. Can you please advise?

  4. Axel says : Reply

    Hello Paul,

    thank you very much for your great video!
    I have a problem with a different dryer – but exactly the same heating system. I tested the three sensors and they are working fine. But I (maybe) found a problem by testing the heater.
    The connector plug has a black, white, red and two brown cables (just like the one in your video). I have done the continuity test:

    COM on black cable. Signal on the white cable and a signal on the red cable.
    COM on the white cable. Signal on the black cable but no signal on the red cable.

    Does it mean that one circuit is damaged and the heater has to be replaced?

    Thank you very much for your help!
    With best regards

    • Hi without knowing the make and model and also having the heater in front of me it is very hard for me to say which is the high heating circuit on which is the low heating circuit .
      You should always have continuity across the neutral going to the high heating circuit and the live, and the same on the low heating circuit.
      if either of these are open circuit then you have a fault with the heater.

      photo  
      Paul Charmbury
      Appliances Engineer
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  5. Steven Mchugh says : Reply

    Hi Paul

    I have the model you are working on in this tutorial and have a faulty Thermistor/NTC Sensor on the rear of the heater, do you know the part number as I’m having problems finding it? is it available via your site?
    Whirlpool AZB9750

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