We have a similar issue with an oil combi boiler. There is a pressure gauge in the boiler which can be adjusted to somewhere around 2 bar. You should have a presure gauge somewhere which can be adjusted.
If anyone can advise on why I'm losing pressure from 2 bar to 0.5 bar within hours. I've looked for leaks but everything seems ok.
Any help appreciate.
Scott Cummings, October 2008