Hotpoint WDL540 washer/drier is playing up

Of course, insulation tests were done right at the beginning, and there are no problems with the motor.

I originally thought that the front panel PCB was only there to decode the button and knob settings, and light the leds via serial communication with the main power board. But I have now dismantled the front panel and found that the PCB contains a full-function 16bit microcontroller (MCU) with a large ROM which must hold all the washing programs. It has an I2C interface with the power module, so sensor and diagnostic information must be sent to the front panel from there, and it is the MCU on the front panel PCB which then tells the power module how to control the various components like motors and heaters.

I could kick myself for not dismantling the front panel sooner. It is now clear that commands are getting from the front panel to the power module to do things like operate the pump and water valve, but it is not receiving anything back from the power module. That is why I did not get any error codes via the leds, and why it would try to do things like fill the drum briefly 3 times and then shut down. If I can't find which component has failed on the front panel, I will have to replace it, but I don't think it is the MCU because it is responding to buttons, and controlling the leds locally in the correct way.

This information may be of interest to others that have experienced similar confusing malfunctions.

My advice, if everything physical (motors, heaters, sensors) seems to check out OK, to suspect (replace?) the front-panel unit first, before going to the difficult and expensive job of replacing the Power Module.

It's always a gamble replacing either the main PCB or the front control panel. They are both parts that can rarely be seen to definitely faulty. Even if they can be seen to have bits burned out you can't know if other components in the machine have damaged them. There's no way to put a meter on a pcb and they come up either OK or faulty. They are normally diagnosed by process of elimination, but there's always the possibility that a weird connection or wiring fault somewhere is causing the fault - or that one or both boards need replacing. Then we have the added problem of manufacturers sending replacement pcbs out with no programming on them. You have to have specialist equipment to install the software onto them. Finally we have the high prices of them and no return policy.

Basically the pcb's are something to steer completely away from unless an engineer or extremely confident electronics engineer. Even many independent engineers don't have the equipment to program some of them because some manufacturers make it very difficult, expensive, or impossible to get them. A white goods engineer can always at least use the pcb on another machine if they fit one and find the fault hasn't cleared but a DIYer will be stuck with one.