Thirsty Hotpoint WM64

I was told the machine was not draining and there was indeed a couple of inches of water lying in the drum. I did the usual, drain manually, check the filter trap and open up the pump but everything seemed OK. I put it back together and tried the machine, whereby I found the real symptom 😳 . The machine is filling up with hot water whenever its draining. It is only the hot so I turned the hot supply off and it works OK (apart from not filling on higher temp. programmes). I’ve not taken the timer/module off to check for visible damage but could see scorch marks on the On/Off switch spade insulators. I will return and fit a new switch but could this be related to the erroneous filling problem? The fill levels for wash and rinse seem OK and I would have thought any problem with the pressure switch would affect the cold and the hot. The customer uses liquid in a ball in the drum and is happy enough to only use the E wash, which still fills up OK, so I would guess if the solution is expensive they will just work away with the hot kept turned off.