Hot water tap for the bath not working properly?

Hi Guys,

Hoping someone can give me some sensible advice. I've got a combi boiler(Valliant TurboMax), and it seems that when I switch on the hotwater tap for the bath, the pressure of the water just comes out ok at start but then dwindles into drops (after 30 secs in). However when I run the hot water for the sink in the bathroom, that works absolutely fine.

Both the sink and the bath are connected to the same hot water supply(pipe, bath being the first in the chain), it seems when I turn the sink hot water tap on, the boilers "green light' starts flashing, but when I do the same for the bath, the boiler green light doesn't flash.

Any quick remedies out there?I've opend the tap up to see if the washer was loose but couldn't find a fault-this rig was working fine about 2 months ago. Finally pressure on the boiler is 1.5 bar (I had to up it from 0.5)

Cheers

Jalz