Cold Radiators

[birdos]

Hi There,
Baxi Boiler, 5 upstairs radiators, 5 downstairs. 22mm Feed and return pipes with 10mm connections to radiators.
I have a central heating system which has been working fine for the past 10 years or so but has developed the condition where the some of the downstairs radiators are cold.(The two nearest the boiler work fine.)
I used to be able to clear this by shutting off all other radiators but this time this did not work.
I have fitted a new pump thinking that may be the problem but no luck.
There doesnt seem to be a blockage as I can drain water out of these radiators through either the feed or return pipes.
I tried clearing sludge using a proprietory cleaner but as the water isnt circulating around these radiators it's to no avail.
Any suggestions would be gratefully recieved.
I m a bit stumped

 

[Softus]

There doesnt seem to be a blockage as I can drain water out of these radiators through either the feed or return pipes.

If you're satisfied that the pump is working and healthy, and that there is no blockage in the pipes to or from those rads, then the only remaining possibility is that the rads themselves, or the rad valves, are blocked.