I have an underfloor heating system downstairs and a radiator system upstairs, the radiators all run from a central manifold. The heat input is from a pellet boiler with internal pump, the UF circuit has it's own additional pump. When the underfloor heating system is on I cannot get heat to go into the radiator circuit. I have tried balancing by turning the flometers down on the UF heating but no go. If the UF is off the radiator circuit works OK but the flow isn't great. Can I add a circulating pump to the radiator circuit. I was told it might work against the pellet boiler pump. I used virtually the same setup 10 years ago and it worked great, the only real difference was I used an oil boiler.