baxi combi 80e systemis pressurising when heating is off

[bernard@gbbikeleathe]

when my boiler is cold the system very slowly creeps up to 3bar the the prv valve is dripping. Top up link has a ball valve and a check valve fitted.
Does not appear to be letting by. Also we have a cold water storage tank in the loft this keeps dripping ball cock valve not letting by.
some how the hot water is connected to the hot water system? we have got mixer taps but I just fitted non return check valves still happening.
Replaced "o"rings and cleaned the diverter vavle made no difference
Could it be the hot water heat exchanger has developed a pin hole inside the exchanger?
Any other thoughts please.

 

[terryplumb]

If you have a combi boiler ,what does the tank in the loft feed ?

 

[cross thread]

Start by disconnecting the filling loop

 

[gas112]

if your certain filling loop not passing then your plate heat exchanger is pinholed and letting mains water pass to heating side and needs replacing