I have a vented oil fired heating system fitted with Grundfos dual headed circulating pumps and Grundfos pump plan wiring centre. There are no motorized valves in the system. I have just fitted TRV's to all the radiators and am going to fit an ABV between the CH flow and CH return. Does this have to be put immediately after the pump or can it be put in farther from the pump? It would be much easier for me to fit it between the flow and return pipes feeding the rad in our spare bedroom .