Hi Guys

I am experiencing a strange problem with my bath mixer tap. When I run
the hot water the pressure seems to suddenly drop off and it slows
down to a trickle. I then have to twist the tap more till I get more
water coming out of the tap. This even results often in the water
gushing out all of a sudden due to the earlier pressure drop off being
somehow released. I am unable to figure out if this is a pipe problem
or the tap problem or maybe even the combi boiler ?
Any thoughts appreciated. I haev tried my best to describe this
problem.
Cheers guys