Bosh SGS5002GB/07 Poor Spray Pressure

Been doing some diagnostics on my dishwasher that is cleaning really badly.

I ran it with the door open a bit and it didn’t even have enough pressure to get me wet :-).
Certainly not driving the spray-arms round.
Reading other posts here I thought was most probably looking at the main motor or, if I’m really, lucky; a capacitor.

My question though, before I start taking it apart, is this;
I know some models have a flow divertor; that alternates the flow between the upper and lower spray-arms. Well mine are both “on” at the same time at the moment. So I was wondering whether this could actually be the problem. Perhaps the divertor was stuck in the middle with both half-on. If so I’ll probably have to replace the instantaneous water heater – a pain but less than a motor!

So does anyone know if this model (SGS5002GB) is meant to run both spray arms at the same time or not?
The water heater part code would seem to be 263187.

Many thanks
Colin