Help understanding circulation pumps

Just wondered if I could ask about how circulation pumps should run? I have a pump (A) circulating between heat pump and buffer tank. Then two circulation pumps (B & C) that circulate between buffer tank and either radiator circuit (main house) or underfloor heating circuit (extension). Presumably pump A should run whenever the heat pump runs and switch off with the heat pump when the target flow temperature is exceeded? Should B & C continue to run even when A is off, to distribute heat around the building? And what (if anything) should be the trigger to B & C switching off? FInally, should B & C run independently of each other, depending on whether the Mitsubishi remote room thermostat (main house) and/or Nu-heat UFH stat (extension) is calling for heat? Thanks.

Hello @HollyCottage

Does the buffer have a temperature sensor in it that runs back to the main controller? and do you have a FTC6 controller? There are two 2-zone configurations:

Thanks @TrystanLea . No temperature sensor in the buffer tank. Only one (apart from the monitoring kit ones) I can see is on the return from buffer to the heat pump? Yes, think I have an FTC6