This is a tricky one without actually looking at your boiler but it could well be the heat exchanger or if you have recently had any new install for your kitchen which may have required your mains being re-plummed, ensure that the cold feed from the stop tap hasn't been accidently connected to the hot supply, it sounds stupid but I have come accross it many times and if your cold is coming out slower than it used to then that's your answer. Hope that the case.
Wayner, September 2009
