I have this shower, just used it and cold water kept coming out after I'd finished.
A visit to the loft established there was just one pipe feeding it.
In the boiler cupboard there is a hellish nightmare of pipes, switches and mystery items.
My understanding is that this black box controls the shower, and indeed by half turning the valve on the top pipe, the shower stopped.
So, is it likely that the black box has a faulty washer or could the electronics be faulty? Just bang in a new box and all good?