Radiators in the basement do not get worm

[Joe ZImmerman]

Two out of five radiators on the basement level do not work. The other three radiators in the basement and all other radiators on the first and second floor work fine. When I bleed them, the pipe at the entrance side starting to be worm. the The boiler is located on the basement level, and the pipes connected to those two radiators run in the ceiling and go down to each radiator. I tried to set the circulating pump to work constantly even when the boiler is off, in the beginning it did not help, but after few days the radiators started to work, but stooped after few hours. I looks like it has something to do with the water pressure in the system that prevent the water in those two radiators to flow.

Any idea what can be the problem?

 

[An72]

You must check first before anything else.

 

[Pledger]

If I read this correctly, are you saying that the pipework from the boiler runs up to the ceiling before coming down to the rads (like an upturned "U") without a tee in the boiler feed to the upper levels so that air can rise? If this is so, then I would be very suspicious of an airlock in the top section of the pipework in the ceiling. If this is not the case then suspect that these rads, being the lowest in the system, may be blocked with debris or silt.
Most combi systems run at a pressure near 1.0 bar but will withstand running at 1.5 - 2.0 bar, if you increase the pressure (to compress the air in the lock) do the rads get warmer? this may or may not prove the theory, don't forget to reduce the pressure afterwards!!