No hot water?

do you mean no water comes out of DHW taps at all?
do you have a hot water cylinder?
if you do have one try tapping it
it should NOT make a hollow sound
if it does make a hollow sound you need to check your cold water tank to see if its got any water in it
[is tank water filthy?]
if tank has water in it, try blowing into cold water feed pipe with a small length of garden hose to clear any blockages
if no water in tank, check ball valve
sometimes they stick in upward [closed] position
if you dont have a DHW cylinder , then cold mains filter to boiler could be blocked
i could give you a precise cause of fault if i have enough detailed information to work with
otherwise i have to be as vague as the question asked

manwithnoname
May 2011