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.
Sorry the pressure switch didn't fix it.
I hope you figure it out.
Now I have a spare pressure switch, for any pressure switching I want to do in the future.
I worked out which relay controlled the heating element, desoldered it, ran some current back and forth through it a few times while testing it's switching peformance and didn't find anything wrong with it, but when I soldered it back onto the PCB and turned the machine on, the machine behaved normally, filling with water and rotating the drum back and forth to agitate clothes, without giving any error code. It might be that the relay contacts lightly welded themselves together at the same time as the PCB trace burned out, and that I unstuck them while testing it.
Things kind of went south when the machine wouldn't stop agitating and move on to the next part of it's program. It turned out that one of the connector tabs for the heating element was broken internally, so no power was being delivered to heat the water. Now I'm going to see if I can fix the heating element, and I'm hopeful that everything will just work after this.
phobia.