I wish to be able to circulate the water in my central heating system without the boiler being turned on (so I can use the under floor heating system as a heat dump). My question is do I need to need to isolate the boiler so the secondary pump does not force water into it. Or its it just fine (like the underfloor heating pump is, just being turned off when not wanted). As I wish to connect the pump in series with the boiler so it can also be used to aid the flow also it will mean it is impossible to create a reverse flow into the boiler, I plan to make a bypass for the boiler which I can activate with a motor operated valve, Is this enough to avoid damaging the boiler pumped or should I fully isolate it using more valves, if so do I need to protect both the flow and return? I don't mind doing things that are needed however I do not wish to make things over complicated.