low water presure in hot water?

i have just changed my bath and sink in my bathroom the hot water is not flowing as well as it should be at first i thought the good old air block !!! but i have tried every trick in the book with no luck,on the old bathroom suite i had just normal taps and now i have nice shinny mono blocks that dont work properly... the hot water is feed directly from a emersion heater and i have even lifted that up by a 1000mm to try to increase the water presure and that has not help...talking of help has anyone got any ideas !!!