Bosch won’t move past wash cycle and I’ve tried the obvious.

I’m having a problem with a Bosch WFXI2840GB/01 integrated washing machine and I really need some help.

Syptoms:
On a wash cycle (e.g. 60deg Cottons) the machine fills with a small amount of water. The timer counts down normally but the machine does not move beyond the wash cycle. The water does not heat up. It continues to wash without heating until you stop the machine.

On a rinse cycle the machine fills with almost half a drum of water and rinses the clothes normally before moving on to the normal spin cycle and finishing.

What I’ve tried:
Intially I thought the heater element had failed so I replaced the heater element and also the thermostat NCT at the same time. This had no effect.

I’ve removed the whole bottom assembly (drain, pump, pressure chamber) and cleaned it all out and re-assembled it. It had a small amount of sludge in it but not enough to cause any problems. This had no effect.

During the wash cycle I’ve tested the voltage accross the heater element and it is always 0v.

Can anyone offer any advice on what to do next. I had thought that the pressure switch was the most likely but that looks less likely given that the rinse cycle seems to work normally.

Thanks in advance for any help.