radiator problems

[wendymunro]

I've bled all my radiators and put the pressure back to the normal indicator on the boiler, why are a couple of them hot at the top but only aired at the bottom? Could it be the thermostat??

[gasman]

No it will not be the thermostat. It is more likely to be due to a build up of sludge and silt in each rad resulting in what we call flat or cold spots where the water is prevented from circulating around the rads properly and thus not heating the rad up uniformly. the only cure is to flush and clense the system.

[wendymunro]

The 2 radiators in question seem to be red hot one minute then hot at the top & warm at the bottom, would this happen?