radiators get cold

[jamborta]

hi,

I have this strange thing about my central heating recently. after shutting down some of the radiators, and reopening them again after a while, they don't get warm any more. I tried bleeding them, and it seems that some warm water gets into them after draining out some water from the radiator, but after a while it gets cold again.
any suggestion would be appreciated.
thanks a lot.

 

[HootingOwl]

when you shut the radiators down, did you turn the valves on each side of the radiator? or just the valve on one side of the radiator?

are all the radiators cold or only the ones that you shut down?

 

[Aquilani]

Do the radiators have Thermostatic valves? perhaps these are stuck.