Vokera Linea 24 combi boiler.
Boiler starts up fine. Water heating fine, although preasure does gradually drop over time.
However when the central heating is turned on, the preasure goes very high. Radiators heat up very quickly..which is great.But then water drips out of emergancy release valve. Preasure drops quickly and system has to be turned off and re-preasurised.
Radiators have been bled, and no leeks visible.

KDCHAD, November 2010

It sounds like the expansion vessel needs either recharging or replacing if it has perforated.to test it let all pressure out of the system and put a foot pump with a pressure guage on it if it reads 0 then it will need recharging to bout .75-1bar.make sure something is open when doing this

MR P, November 2010

Boiler expansion vessel needs recharging/replacing

Carefree, November 2010