Strange issue with a hot tap (mixer)

[Smcart5]

I have a mixer tap on the kitchen sink which seems to have a problem on the hot side where the pressure drops drastically a few seconds after turning the tap on, i posted about it and the pressure was apparently because the combi-boiler only allows a certain flow rate of hot water through and adjusts after the tap is opened.

Its now gotten much worse, the hot water tap now turns off completely with a loud thud, and sometimes it does this a second time after i turn the tap on more, it seems i can only get a tiny trickle out, or full pressure (not ideal for rinsing plates).

Mid-way and the tap will stutter like a pneumatic drill and be almost as loud, i can't seem to get a moderate flow out of it, considering hassling the estate agent again for a plumber but i am curious as to what might be causing this, any ideas

 

[Billy Bob Bob]

knackered jumper and seating in the tap,either tap converters or a new tap to sort it out

 

[Smcart5]

By jumper you mean the tap body?, the seating was grinded before it was replaced last time.

 

[Billy Bob Bob]

its probably wear in the valve its self tap refurb kits[new valves and heads ] only cost£9 for acrilic heads