My boiler is not heating all the heaters.
it's the heaters that are farthest away from the boiler that are not heating. If I increase the speed in the pump it gets worse.
The boiler is about 25/30 years old with a header tank in the attic.

James, December 2012

were they all warming up before if so then it may require the system to be cleaned by the use of a chemical or the pump may be worn out. u can also adjust the rads that the ones are warm turn them down on the lockshield valve side this will increase the pressure to other rads do this bit by bit and until all rads are a constant temp

kash, December 2012

Yes they are all full of water

James, December 2012

Have you attempted to bleed the rads with no heat?

A1, December 2012