Solved the problem in the end.
I had a look at the old cylinder last night and you are right, strange coil inside so must be one for gravity. I do believe it was the original one.
Going back with a fresh mind today I noticed the vent pipe was a little low, the top only 25-30 cms above water...
I dont think so, there is a check valve on the flow and is going the right way.
To describe the system (HW side) a little more. I suspect there was an old floor standing boiler, ideal Mexico or such, in the garage that was probably one of those that used convection, then pump only fired for...
Hi, I just put an indirect cylinder in for someone, simple one in one out..or so I thought.
When I fire up heating and hot water all is well, when hot water only is selected, the water from the boiler spills over into to f and E tank in the loft.
I've tried turning the pump down but it still...