so I took a job on to finish another plumbers boiler as he had walked off site, to cut a long story short , as I was filling the system up with the external filling loop I noticed the pressure gauge wouldn't rise .......... not one bit!! Worcester combi it was, so I opened her up , everything looked connected , the prv wasn't discharging so I assumed there was not much pressure coming into the house, as I could nearly stop the mains at tap with my hand. I didn't have my pressure clock in the van so couldn't test the system pressure. so I informed the builder of the problem , and told him the bad news that the system wasn't suitable for the incoming mains, and I would look to see if there was something to boost pressure available, he was now somewhere between mad-angry-crying-crazy-shouting-swearing on the phone with me, as the house was all finished, and the cowboy plumber had ran away with his money before finishing etc. anyway when I was there tonight I found the problem , very embarrassing for me, I didn't tell him what it was, and told him it was just air trapped in the pump and its ok now as I was able to top her up to 1.5bar. now first to guess what my problem was!!!!!!? but don't tell anybody as I might have to go back to yr 1 in collage and loose my gs and tools if anybody finds out lol!!!