New answers tagged water-circulating-heating
One partial answer is to deliberately decouple the pex from the floor. E.g. if you have a crawl space, mount the pex a couple inches below the subfloor. Fill in the joist space below with paperbacked 4" insulation bats. (Less if you want the crawl space warmed.) The Pex now warms the air, which in turn warms the subfloor. This gives more even heating, ...
You probably have a airlock in the pipes leading to the 3rd floor. If water can come out when you are bleeding then there is enough pressure. Close all other radiators and see if that will clear it. Otherwise the return pipe is not connected properly or just clogged. That is harder to fix.
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