How a NTC Sensor works on a Tumble Dryer

by / Saturday, 13 December 2014 / Published in Heating Systems, Tumble Dryers




Tumble Dryer parts Ntc Sensors

Tumble Dryer parts Ntc Sensors

 

The temperature is controlled by the PCB by means of a NTC temperature sensor, when you test it the Resistance drops as the temperature rises.




The NTC sensor is normally fitted to the hot air fan duct. 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. 

NTC sensor

NTC sensor

What is an Tumble dryer NTC Sensor?

A Tumble dryer 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 Tumble dryer because their electrical resistance at various temperatures is known, it’s easy for the Tumble dryer to monitor a thermistor and detect when certain temperatures are reached.

Check all connections first to the 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.

6 Responses to “How a NTC Sensor works on a Tumble Dryer”

  1. Brucklacher says : Reply

    Hello,

    we have a Privileg 20403 dryer. The error is E66.
    Waht could I check or what could I change.

    Dear
    Hardy Brucklacher

  2. Kevin says : Reply

    Hi Paul

    TDWSF83BEP Door Filter Light

    Im looking for a little assistance into a tumble dryer fault please and the spares i may need. The door filter light comes on, if you push start machine comes back on again but then soon cuts out again with the red light on. So i have investigated and the following has been done.

    Tumble dryer does get warm but keeps cutting out with red door light.

    I dismantled door filter and cleaned any lint debris from filter and duct.
    I removed condenser and cleaned under tap as per instructions found on line.
    I removed right side of machine and found lint under the NTC sensor by fan motor, removed this lint as thought this was problem, but machine still does the same.
    Opened covering here as well and cleaned any lint from here, only minor.
    Removed rear heater to look to see if heater had any lint, but hardly any found.

    So tested the sensor on top of heater and the thermal fuse, thermal fuse has continuity and sensor has resistance circa 18k Ohm that reduces when warmed as expected, heater tested (not expected faulty as was getting warm) and both coils ok.

    tested sensor by fan motor (NTC?) and again this has a resistance and reduces with warmth.

    So I inserted a thermocouple close to the two sensors at top of heater to see what was going on and when you start machine it appears to turn heater on which rises to circa 250 Deg C this then reduces down to circa 30 Deg as fan cycles air through. It tries again to heat and it goes to circa 340 Deg C but then stops and lights the door filter light.

    Removed and reinstalled connections to pcb by selection knob but no different.

    I guess the thing is cutting out because it thinks blocked by lint and overheating but sensors appear to be ok,any help with spot where my thoughts are wrong please and what to test to understand what i need to purchase to repair?

    Thanks V Much

    Kevin

  3. Kamil says : Reply

    Hi there
    I had an engineer to check my washer dryer and it was PCB unit which I’ve replaced and now it’s showing another error t3E but the temperature sensor in the drum is fine. is there another sensor in a duct?

  4. Robert Soldan says : Reply

    Hi,
    on mime Hotpoint dryer the NTC thermistor has like 350k ohm resistance, decreasing when heated,
    is it possible to be so high? should be liek 20k ohm or so?
    thanks

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