Gainsborough 8.5SE outlet pipe gushing water when turned on.

andy2004

Gainsborough 8.5SE outlet pipe gushing water when turned on. through what looks like a overflow/water pressure hole as its against the wall.
well its says 8.5se on the top of the shower but on the website it looks like the 9.5se model.
http://www.gainsboroughshowers.co.uk/parts-store/Gainsborough-Showers/Gainsborough-95-se/
Monday we had a plumber out to look at our combi boiler as we had no hot water and they fix it, low pressure. today whilst cleaning the bath out i decided to use the shower to rinse the bath out, and turned the dial to cold and turned it on, then noticed the water was not only coming out of the shower head but also against the tiled wall. after taking the front cover off, i turned it back on again to see where the water was coming from, and it was coming out the outlet pipe but not only out of the shower head but out of the other hole aswell.
the outlet pipe is where the shower lead + head is connected but there also looks like a pressure tube aswell.
http://www.gainsboroughshowers.co.uk/parts-store/Gainsborough-Showers/Gainsborough-95-se/Outlet-Pipe/
Is it a simple valve inside the pipe which didnt go back, or is it a thin piece of plastic which due to the pressure has now broken and therefore the actual outlet pipe needs replacing.

what a dumbass i feel, after taking a further look at the pipe with a torch, i found out inside theres a little plastic ball, taking a small screwdriver i pushed the ball back in the overflow part, and then tested the shower again. no water coming out from that bit of pipe.