Hello guys, I looked at heating system yesterday. A large 2 story house with 2 story extension at back. The rads to extension never worked. Its a 90,000 btu oil fired boiler. Pipes from boiler are 22mm (should be 28mm) coming from shad near house. From what I can see I think flow and return for extension were teed into the existing flow and return undreground between boiler and house. I might put in a stronger circulating pump. If that doesent work, would pressuring the system make a difference to give system equal pressure.