Glow worm Betacom 24c no hot water but central heating fine?

Hi,
I had a new boiler fitted about 8 months ago, everything has been working fine until last week, now for some reason my water will not run hot, it just runs hot for a few seconds then goes warm! The central heating is working fine and the 30, 40, 50, 60,70,80 lights are all coming on however when i turn the shower on the lights one by one switch off, any help would be really appreciated as cold showers in the winter are not much fun!!
Thanks in advance