pressure drop sabre/vokera combi

[sam65]

Hi guys, Can anyone help with this problem?

My Sabre combi is around 3yr old. I'm getting a pressure drop to alomost zero when my heating is off. I pressurise the system to allow the boiler to fire up (I have a leak somewhere?). When the boiler kicks in the pressure increase (I'm now up to ~3Bar!) I've turned the CH off for now.
Any ideas on poss cause?

Thanks in advance.

 

[chrishutt]

Expansion vessel. It's covered in the FAQs.

 

[sam65]

Chris,

Found it, Cheers.