Bendix d/w DH102 Pressure switch not resetting

PNC 91183102700

Help!!! I have spent hours on this machine!

Customer complaint is heater coming on with no water. On inspection the pressure switch is not resetting when the water level drops.

I have cleaned out all of the pipes and removed and cleaned out the matrix.

There is a little discolouration inside the IWMS but no physical blockages.

The appliance works ok when cold but will fail after a heat pause. (only after I have left of course). I assumed that it might be sticking contacts in the pressure switch but a replacement pressure switch does not cure the fault.

I have watched it through a cycle and it actually failed when I was there!! Thank God!

When the water level in the machine drops during pumpout, I can see the level drop in the IWMS but it does not suck the water out of the chamber that pressurises the pressure chamber. Confusing thing is, it works fine when cold but not when hot???

Do I need to fit a new IWMS or am I missing something?

Bob