halstead ace 30 he

[totalshell]

head scratching on this one... boiler in good condition serviced every year etc. water pressure kept rising on ch so all normal checks done on system expansion vessel seemed to be ok at 1 bar absolutely zero water expelled from Expansion vessel valve, water circulates freely around rads, all heat up quickly and to a similar temperature
but water pressure rises slowly (20-30 mins) from 1 bar to just under 3 before the prv kicks in and starts letting by.
halstead advised that pipework to expansion vessel most likely blocked,,
added auxiliary expansion vessel to circs, found tin lid from fernox/ sentinel bottle in magnatex
set ch to full water at 1 bar cold new vessel at 1 bar temp control set to max filling link disconnected and watched for 2hours pressure rose to 2 bar . ch switched off on customers request as its the middle of summer
that was 3 weeks ago customer now reports that pressure rises even under DHW only,

any experience/ ideas appreciated.

 

[heatserve]

Perforated plate heat exchanger. If filling loop is disconnected and boiler not running, can't think of another explanation - unless someone has connected a tap to a radiator or something