vokera linea 35,pressure goes to3 bar when heating is on?

Expansion vessel problem, may need repressurising or replacing. Drain system and re pressurise with a foot pump to about 1 bar ( installation/service instructions will confirm exact level) Could also be too big a system for expansion vessel, usually good for 7 or 8 rads if you have more may need an additional expansion vessel.

Peter
January 2009