Boiler bought 20/12/06, installed in January 2007. Been fine but this week has developed a fault. When the CH comes on the pressure continues to raise to beyond 3-3.5 bar and then the system starts to reduce the pressure by emptying the water outside. Subsequently, the pressure drops significantly and develops an 04 code fault (low pressure). HW is fine - problem only occurs after switching on the heating. Vokera are still covering this with their bog standard 2 yr warranty (so parts and labour, I think are covered) but, having spoken to their helpline, they've suggested it actually only needs a service as the fault sounds like "no air in the expansion vessel". They could service it (at cost) in April for me! My own plumber thinks there could be a fault with a valve or pressure gauge and would fix at cost (parts & labour). Anyone have any idea of the cause? I'm a non-technical person but if there's a fault I'd rather not pay to repair if it's still under warranty ! Meanwhile.... no heating ! Thanks.