Hi well a quick up date, because of the body round the engine in hymer , its hard to get to the vacuum pump so managed to take the pipe of it and bingo, reading 24" but most importantly it was instant so with it been a bank holiday cannot get any parts for it, so repaired it with a glue that takes 12hours to set, so will start her up tomorrow and hopefully will run OK, will let you know if all OK, as if is OK will of saved 100s in garage costs, Dave