David Lang wrote:
Hi Chris
Inside the case (well, when you take the top cover off) there is one
adjustment, a spring loaded plunger comes out of the high pressure
delivery connection and pushes something inside the plastic box which
also has the On/Low/High control going into it. This plunger can have
its length adjusted. Can anyone explain what it's for and how it
should be adjusted?

First of all, I assume that when conected to the tap water flows through the
machine and the nozzle isn't blocked? I don't know this particular machine,
but.....

Yes, flows as freely as it always did.

Normally these machines switch on and off with a simple pressure switch.
Assuming the working pressure is 100 bar, there will be a spring loaded
valve set to (say) 110 bar. When the trigger is closed, the line pressure
increases, forcing the valve to open.

The valve has a piston or rod attached and when the valve opens the rod
moves. The rod pushes a micro switch and breaks the circuit, so the motor
stops. When you pull the trigger, the line pressure drops, the valve
closes, the rod moves back and the micro switch makes the circuit again.

If the machine wont start it's usually because;

Valve is stuck in off position - very common if the machine hasn't been used
for a while.

It stopped working after I'd been using it for a while so that seems
unlikely.

Valve set to lower than line pressure.

First thing to do is check that the spring loaded plunger is free to move &
not stuck. Can be limescale or detergent residue, so if you can get it
apart, clean it, lubricate it then it should work.

Failing that, try adjusting the plunger length. A small adjustment makes a
big difference, so don't go mad! Or the microswitch is u/s. If the motor
hesitates it's posible the start capacitor is faulty

My guess is that the plunger is simply stuck/sticking.

Thanks for the explanation of how it works, all pretty straightforward
really. It definitely feels to me as if the microswitch is simply not
being operated. The plunger seems quite free though so maybe I'll
take a look at the mechanics of how the plunger operates the
microswitch. There is a minor added complexity in that the washer has
a rotating 'switch' with OFF, LOW and HIGH positions, this has a shaft
that goes into the same place as the plunger (e.g. where the
microswitch is) so it may have some clever interaction with the
plunger to adjust the output pressure.

--
Chris Green