So today ive had a heating engineer out to find out why now ive put the heating on some of the radiators are cold. After spending a while trying to balance the rads etc he has said that the system needs a bigger heating pump in the airing cuboard. So the heating system has had a lot of strain and the size of the networks has increased massively due to a large loft extension and also a large single story extension. Counting up theres 20radiators in the house with many of them being large double panel vertical rads. In the bathrooms are large floor to ceiling towel rails weve had put in too so the capacity has increased a lot. The current pump is grundfos 15/60 130. Kids what size pump will it need now? The engineer has gone away to find out some more info and is goin to come back to me as he couldnt tell me what size pump the system will need just said a bigger pump.