Grohe shower problem

[chrisbg02]

I have a grohe (1000 i think) shower which is fed from a combi boiler. It has worked fine until about two days ago and now i am getting very little or no hot water. the taps in the bath and sinks are all fine and giving plenty of hot water, boiler has recently been serviced and is all working ok. has anyone got any ideas what the problem could be please? Shower was fitted 12 months ago and has worked fine until now!!