I have 2 rads on the second floor that will get hot water flow only when I stop all flow to the other rads on the system. Even then, the flow is very low.
I have had this system for 10 years and this is a new problem. I have bleeds on each rad, and there does not appear to be an air lock, anywhere.
I am wondering if it may be the circulation pump, or the pressure regulator. I don't think it is corrosion that is shutting down flow to both second floor rads simultaneously. Each rad has dedicated piping from a T off the boiler.
When I remove the bleeding cylinder from each rad on the second floor NO water flows out, unless all other rads are shut off.
Is it pressure in the system that gets water to the second floor, or is it the pump?