Hi Dave, I've done everything you've suggested and heat gets to the manifold and into the beginning of the infeed. The outfeed pipes aren't warm but that can be expected due to heat transfer. However, the floor doesn't get warm even leaving everything on for days. As an engineer I understand how the system works but don't understand how to isolate the return manifold. This is partly due to the fact that it's very difficult to trace where the pipes go in a 400 year old cottage.
The circuitust have been filled initially so I'm assuming that the return manifold can be closed off. I've tried shutting off the Magnaclean unit and hooking up a hose, etc but when I shut off the supply from the hose, which should mean no water flow in the system, there's still water coming out of the return manifold. I can only assume that it's back flowing or syphoning from somewhere else.