Radiators cold at the bottom

[AlanWright]

I recently changed taps in bathroom. I turned the cold water off at mains and closed all valves in airing cupboard. When I tuned everything back on most of my radiators would not get hot. Upstairs a couple were ok but the rest were warm at the top and cold at the bottom. Similar story down stairs but a few don't even get warm at all. Tried closing off radiator valves to force the water through other parts of the system but with no joy. The pump is ok. Any ideas?

 

[Hudd3]

Have you fully opened a manual bypass valve?..... connects flow and return pipes and should only be very partially open.

 

[gas4you]

As a general rule rads cold at bottom usually indicates sludge build up, especially downstairs ones

 

[AlanWright]

Have you fully opened a manual bypass valve?..... connects flow and return pipes and should only be very partially open.

Thanks for your help, I think this is the problem however I am not sure which valve to adjust. Is the valve always in an obviouse place or position relative to the hot water tank or pump? I have five valves all in the same area ie the airing cupboard.
Regards,
Alan Wright