Hi All, 1st post, like the site. Removed tanks, cylinder and conventional boiler, heating pumped, domestic gravity. Installed Biasi combi, replaced 4 rads (10 in system) installed thermo valves to most, domestic ok but problems with heating not circulating. Then defined heating was a one pipe system. Last week converted downstairs to two pipe and all downstairs radiators work. Yesterday converted upstairs to two pipe system, filled up, fired up, downstairs ok but nothing upstairs (not me, the house). Can only get upstairs to work if all downstairs rads are turned off, but even then they don't get that hot. I suspect the pump. Brand new boiler and system flushed out. Any ideas. Sorry about long post. Thanks