Radiator problem

[missesbell]

With the gas boiler on and the radiators selected, the room stat demanding heat, all the radiators upstairs are getting hot.
However the radiator in the lounge was cold, after a few minutes the feed pipe was too hot to hold but no heat in the radiator.

I checked the one in the kitchen this too was cold, the one in the hall was getting hot.

I turned all three radiators off upstairs in an attempt to force flow of hot water round the downstairs rads, too no effect.

Both the return and flow pipes to the boiler were hot.

I then drained water from the feed pipe to the lounge radiator with the radiator turned off. Hot water flowed easily. I then turned to the return pipe and achieved the same result. I then tried draining water from the return pipe through the radiator with the flow turned off.
Same result, water flowed easily. I then isolated the return pipe and drained water from the feed pipe via the radiator, doing this I achieved a hot radiator.
I then opened the return valve which should have enabled water to flow freely from the feed to the return manifold, it did not.
Note the system pressure did not fall below 1 Bar during these tests and was returned to 2 bar at the completion.

Any ideas??

[TWR]

Dirt in the Valve Misse, Close remove & clean out.

[buildersmate]

An excellent set of tests to help diagnosis, misses.

By turning off the upstairs rads, it should force the water through the downstairs ones, even if the system is 'unbalanced' - so I think we can rule that out, I think.

Can I ask where you are draining water from? - you use the term 'feed pipe', which suggests someone that is NOT the bleed valve that is present at the top of each radiator.

If you have bled water from lower down at your 'feed pipe' you will not remove trapped air/hydrogen (hydrogen being the product of corrosion in the event a system does not have adequate inhibitor). Please answer this point first

If this is the case, I suspect there is no water in the upper parts of your rads.