I climbed into the shower the other day and at first it was working but after a few minutes it had completely stopped. I turned it off and now two days later there is still no water coming through the shower head although, I have hot and cold water everywhere else in the house. Can anyone suggest what is wrong and how to fix it please?

First off you have to determine just where you're losing pressure at. Unscrew the shower head and try it now. Still no pressure? I didn't think that was it but had to Now shut the water off to the valve and open it up and check and clean the inlet ports on the cartridge. Before you button up turn the water back on for a moment to flush out the supplies. If you have water form the supplies reassemble the valve and try it now. Good luck, Tom