Worcester greenstar combi boiler not heating above 35C?

I have a new Worcester Bosch 30i combi boiler which was installed a couple of months ago, but I just can't seem to get the central heating to go above 35 deg! The pressure is fine, hot water fine, but it just won't allow me to turn up the CH temperature to above 35 degrees, so the radiators are only ever warm, not hot... Does anyone have any suggestions please? I may have fiddled with some settings by accident but can't figure it out at all and the instruction manual is no help whatsoever! Thanks a million :)