why is the new pressure vale still leaking?

Reduce pressure to 1.2 bar,it should not leak if it's new ,you have to return to seller it still leak,if from 1.2 bar when boiler is on full blast for 6 hrs or more it's should stay 1.3 bar if keep rising than it's expansion vessel need air pump in to .75 bar to do it with cycle pump ,with boiler drain out

ltd
March 2013