Bosch classixx5 washing machine WAA12160II

Hello. If it heats on every wash, even on a cold setting, but rinses stay cold, the fault is most likely in the heating control circuit rather than the NTC itself. On these Bosch Classixx machines, the heater is only used during the wash phase, so your symptom fits that.

Before checking anything internal, isolate the washing machine from the mains.

1. Check whether the heater relay on the PCB is sticking on If the relay contacts have welded together, the heater will energise whenever the wash cycle allows power to that circuit. Reflowing solder joints won’t cure welded relay contacts. Inspect the relay area for heat damage and, if possible, test whether the heater is being fed continuously during wash.

2. Check the pressure system Many washers only allow heating once the water level pressure switch confirms the drum has filled. If the pressure switch or pressure chamber is partially blocked, it can give odd heating behaviour. Check the pressure hose, chamber, and switch operation.

3. Recheck the NTC properly Even if it seems “working”, make sure its resistance changes smoothly with temperature and that the wiring back to the control board is sound. A poor connection can make the board misread the water temperature.

4. Check for a heater earth leakage fault A heater can partially short internally and overheat unpredictably. Test the heater for insulation leakage to earth with the correct test equipment.

5. Program selector issue A slow or worn selector switch is worth noting, but it is less likely to cause full heating on all wash programmes than a stuck relay or control fault.

If you are not equipped to test live circuits or PCB components, I’d recommend a qualified appliance engineer. Any mains electrical work should be left to someone competent.

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