oil boiler overflow dripping

[Dawnpipes]

Hi, We have a Grant oil combi boiler. Only 3 years old. Been a right pain. Already had expansion vessel replaced and the 3 bar PRV and another thing that I have forgotten name of, but it has a load of copper mini pipes is a square loop. Then when it was really cold the overflow started chucking out hot water like Niagara falls. Have had two really nice engineers out. One said it shouldn't happen with all the things we had replaced on it, and the other one concluded that it was the cold weather and the condensate pipe freezing. Any way it has worked ok for a bit and now overflow dripping. The pressure goes up to 2 if that helps. Any ideas of what it could be would be really helpful-thank yo

 

[SimonG]

Expansion vessel undersized, blocked flexi to expansion vessel, filling loop passing, etc