I have a problem with my Vokera boiler, when cold the pressure will drop to almost zero, if I top up the pressure to 1 bar and turn on the heating it increases slowly to about 2.5 - 3 bar(at 3bar the PRV kicks in ok)
Once the heating reaches the right temperature (70deg) the burner stops and the pressure starts to fall, once the temp reaches around 58deg the burner starts and the pressure increases again. If I switch off the heating it slowly drops pressure to almost zero over about 30 mins. I found there was no pressure reading from the expansion vessel so I recharged it to 15 psi but problem still persists.

Can anyone help.

Jim, October 2009

My guess is Ian's right. You need to manually operate the PRV so there is no system pressure whilst pumping up the expansion vessel 12psi should do. Download the manual
http://tinyurl.com/ygwvwxo
pdf 30/64:
8.20.2 Close heating flow and return valves (fig. 6) by
turning 1/4 turn until indicating lines are horizontal.
Pull lever on head of safety valve to
drain primary circuit to boiler.

c, October 2009

Ian,

Many thanks for your reply.

No I didn't re-pressurise with the system drain open, to be honest I'm not sure where this is... or do you mean the safety valve, if so how is this opened.
Also is the flexible hose easily accessed?

Jim, October 2009

did you re-pressurise it with the system drain open? if not you need to do that. otherwise i'd suspect that the flexible expansion hose is blocked, it's quite common.

Ian, October 2009