From one day to the other, the machine was not heating anymore. There was power, some LEDs were on as usual, and if I remember correctly, the pump started operating, when the steam valve was opened.
Some quick checks (any cheap DVM will do):
- the heater was ok (conductive between A and B)
- the thermofuse (T) was ok (conductive between A and C)
- the thermoswitch (D) was on (conductive between the two leads)
- the NTC-thermosensor (N) had a resistance of about 110 kOhms (measured unplugged at D)
- There was no mains voltage between A and B after power-on (as it should be).
These findings suggested that the critical parts of the machine were ok and that the problem was somewhere on the green PCB at the right. It turned out by a visual check that one of the contacts where the relay R had been soldered to the board had gone bad (see the 2nd picture, red arrow), there was no connection between the pin and the pad. This was easily repaired with some solder and a hot iron. No need to get a new PCB (if it is still available at all) or even to discard the machine as broken and not serviceable.