WMF Stelio milk frother does not heat up - replace the NTC thermal sensor

ID: 182305

Description: WMF Stelio milk frother no longer heats up....

Steps:

  1. Function check: Operating indicator flashes red. No heating. Press twice = stirring cold is OK.
  2. Open the device: 3 screws on the base (feet). Check the heating loop and thermal fuses: approx. 120 ohms = OK. Relay does not switch on. Power supply to the electronics is OK.
  3. Check the thermal sensor: approx. 600 ohms (no change with temperature change...defective)
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  4. The NTC thermal sensor remains low-resistance throughout, which is why the heating does not switch on. Determine the switch-on value using a test potentiometer.
  5. The cut-off point is determined by repeated testing (starting) while changing the resistance value: 30 kOhm, i.e. the electronics switch the heating off at R<30kOhm and turn it on at R>30kOhm.
  6. A suitable NTC is one with R25=100KOhm and B=3950K. This has approximately 30 kOhm at approx. 60°C. (Type: F58-100K-B3950-1%- DO35 housing, a few cents).
  7. New, identical NTC installed in the sensor cable.
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  8. Reinstall the NTC sensor with insulating tubing and thermal paste.
  9. Reassemble the device. Perform a function check and VDE test.
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