Update on my washing machine situation:
I took a chance and bought a replacement pressure switch for it, but that didn't make any difference. I checked the control module PCB for damage and didn't spot anything, tested the thermistors for the dryer and water heater and found them to be ok, checked each of the water inlet valves, the drain pump, drain hose and pressure switch air-hose without finding any problems. I took the program-select rotary dial mechanism apart, cleaned the electrical contacts in it and reassembled it, to no avail.
I then did some more research online and found a post on a forum where someone had found a burned-out trace on their control module PCB and had fixed their machine by repairing the trace, so I took another look my own control module and found a small scorch mark that I'd missed earlier, where a thin trace had burned out. I soldered on a replacement jumper wire, reconnected the PCB to the washing machine, turned it on and was rewarded by the familiar and reassuring sounds of it filling with water and starting the wash cycle as it's supposed to.
A few seconds later, I heard the less welcome sounds of it gurgling to a halt and signaling an error. Now it's flashing it's LED 7 times, which is progress of a sort. Seems that the relay for the heater might be stuck.
