Some of my radiators are cold, but when I try to bleed them no water comes out!
This can be caused by an airlock. Try turning all the other radiators in the house off (using the radiator valves, noting the number of turns each time) and then try bleeding. Reset the valves to their original positions when you have finished (see below regarding 'balancing'). Alternatively, if you have bought cheap thermostatic radiator valves from a DIY shed, or have a system suffering from sludge, the internal pins in the TRVs regulating the water flow may have become stuck down in the closed position. Remove the TRV head (not the whole valve) by unscrewing it, and pull the pin gently upwards with a pair of pliers. Note that this tends to be a temporary fix. Lastly, sometimes central heating systems suffer from a 'blocked cold feed'. This will gradually cause the system to run out of water, because it isolates the water feed and expansion tank from the radiator network. Repairing a blocked cold feed is not a DIY proposition.
How to balance performance throughout the house on different radiators?
This can be achieved by adjusting the lockshield valve (usually covered with a plastic cap) to apportion flow across all the radiators in the property. Professionals usually set these up by checking the temperature differential across the inlet/outlet pipes; however a more basic balance can be achieved by impeding the flow of those radiators nearest the heat source (the boiler) and opening the valves to a greater degree on those radiators furthest away
I hope this helps you fix the problem
Paul (AARRID Plumbing)
Paul, December 2004
