Most members have responded to this thread with a normal domestic system in mind ( as I did ) but if you re read the op he mentions ( a million rads) obviously a slight exaggeration but that’s why I asked how many rads , a system of this size has probably had a multitude of plumbers and heating engineers working on it over its life and they have all probably done what they thought was the best fix to cure the problems as they have arisen. Sometimes although the cost would be horrendous it’s a case of “ back to the drawing board “ to re design the system to make it more efficient and easier for future engineers to understand. Something I mentioned earlier is the quality of the water in the heating circuit, the age and type of the rads fitted, the likelihood of sludge deposits given it’s mainly iron pipe work ( and lots of it ) very likely that at some point a commercial heating engineer will be required to assess and make the necessary modifications to improve the system efficiency. Op says some of the rads are turned off so what happens should they all be turned on? I don’t know a lot about gshp but recognise that similar to condensing boiling if the system is not up to scratch and fit for purpose then any efficiency savings are lost along the way. I’m currently gutting a 6 bedroom house that originally had an oil system / floor standing cast iron rads and large bore iron pipe work with a floor standing boiler the size of a 6 x 8 shed . Too big a job for me alone in terms of size of the property and the time constraints but an x b,gas engineer and friend of mine are likely to go with an unvented hot water system ( solar compatible) and at least 2 possibly 3 heating zones . No easy task as the property has been empty for years.
