Job description

i am having problems with the hot water upstairs on a valiant Combi boiler, its about 10 odd years old, the last work on it was a replacement diaphragm i believe a year ago . The hot water downstairs is fine but upstairs shower has no hot water and the bathroom sink taps run infrequently luke warm to medium hot . would like someone to fix this problem .

* Added 11th December, 2011 :
bathroom taps running fairly cold to luke warm at best now . Pressure on boiler says 1.5 bar . there is a header tank in the loft ( assume this is a F&E tank for the CH? ) . When the diaphragm was replaced the plumber also said there was blockage in the hot water pipe near the boiler which he cleared out, which improved water pressure upstairs ( although hot water coming out of shower head was never 100% , it sometimes blew hot and cold) . The pressure out the hot water taps seems ok at the moment .