Radiator wont work!!

[PaulRB]

Help!! 1 radiator wont work. Turned off all others to force water thru system but no luck. Took off rad and flushed it, turned on valves to see they were working, attached hose from o/side tap to both valves to clear air-lock, replaced rad + still wont work.
However, if I drain about 4 pints from the rad drain off, the hot water comes thru + rad works for 2-3 days.
Took off rad and replaced with length of 15mm pipe and pipe heats up immediately so I assumed the problem was the rad itself.
Bought new rad and installed, and turned on heating. Rad got hot immediately but stopped working after 5 days.
It seems as though the rad won't heat up if I let the system go cold for 2/3 days.
Something must be stopping the rad from heating up but I can't fathom it out and I don't want to keep draining the rad to draw water thru.
Any ideas would be gratefully received!!!!!

 

[tincup]

Hi

Has the system been properly balanced. An explanation of balancing can be found in the FAQ.

HTH

 

[spraggo]

It sounds as though you have an air lock in the pipe feeding the radiator,
to check, remove the radiator and with something to contain the water, turn on each radiator valve separately to make sure you get water through each one. Do this with the heating switched OFF.

 

[PaulRB]

Hi

Has the system been properly balanced. An explanation of balancing can be found in the FAQ.

HTH

Thanks. Yeah I know about balancing the system, but how do you explain that the rad wont heat up with all the other rads off?
I thought it must be an air-lock but then, when I drain off about 2 pints, the hot water comes thru!
Frustrating!!!!

 

[PaulRB]

It sounds as though you have an air lock in the pipe feeding the radiator,
to check, remove the radiator and with something to contain the water, turn on each radiator valve separately to make sure you get water through each one. Do this with the heating switched OFF.

Thanks. Done that.

Only thing I can think of is that there could be some sludge in the pipe but that wouldn't explain why I can draw water thru by draining off 2 pints!!

There must be a reason, I just can't figure it out.