I've just recently (two weeks ago) had a new combi boiler fitted, since then the pressure has dropped and turned the boiler off completely, the fitters of the boiler came back and restarted it saying could be just air in the system and it needs to rest. (as I had an emmersion and header tank before) So again it was reset and air let out but yet again the pressure is going down.....Have been told it could be a very small leak in the old pipe work (they and I checked theirs ) and could need some "stuff" put through the system to block said leak (similar to stuff you put in radiator of your car) .....So is this right or could it actually be the new Boiler???? Thanks x