Hotpoint WF440 does not stop filling or draining

[tim_s_uk]

I have a Hotpoint WF440 that starts a wash cycle normally but once it starts filling it does not stop. If I cancel the cycle and start it draining the pump does not stop when the machine is empty. At this point the on/off light flashes with the Mini Load light, which I believe indicates 'f08 heater relay'.

I saw some other threads on here that pointed to the pressure switch, so I cleaned out the sump and pressure tube. I can feel the pressure to the switch increase when the machine is filling and drop when the machine empties, so the tube appears fine.
I tested the contacts on the pressure switch when blowing in to it and can confirm they change as expected (two contacts change over for light pressure and another closes for overfill pressure). Despite the pressure switch appearing OK, I replaced it, but the behaviour is the same with the new switch.

What should I check next?
Thanks in advance.

 

[Alec_t]

If the pressure switch operation is ok and the tube to it is clear and pressure-sealed, check electrical connections/wiring to the pressure switch. If those are fine then the problem is likely due to the controller pcb.

 

[tim_s_uk]

Thanks for the reply. I have also found that when I power on the machine and leave it for 1 minute, the on/off light starts flashing with the Mini Load light and the drain pump starts running. The behaviour is the same if I disconnect the pressure switch.

I have had a look at the PCB and I can see the pressure switch connects +5v on the common terminal to diode D16 and resistor R70 when empty, and diode D17 and resistor R72 when full. The voltages at the diodes are good (+5.1v D16 for empty and -0.4v D17 for not full). The voltages after the resistors are similar (3.1v after R70 and 2.64v after R72). I can't see any reason for the voltage after D17 / R72 to be pulled up.

I think I'll have to send the PCB off for repair (£50 on eBay), unless anyone is familiar with the PCB and can suggest something else.

 

[tim_s_uk]

My WF440 is working again. I sent the PCB off for repair, but a repair wasn't possible (the failed processor chip is no longer available). They refunded me most of the £50 repair fee and I bought a second hand PCB instead. Although the replacement PCB is for a WF540P it appears to work in my WF440. It's possible a couple of the programs are now 10 degrees cooler - perhaps I should get a new draw with the correct program details!