The first cold week of November is when everyone discovers the bedroom radiator is warm at the bottom and stone cold at the top. It is one of the easiest things in the house to fix, and it makes a noticeable difference to both comfort and bills.
Why the top goes cold
Air collects at the high point of a radiator and stops hot water reaching it. Bleeding simply lets that trapped air out so the whole panel fills again. You need a radiator key, a cloth and a small container.
Bleeding step by step
Turn the heating off and let things cool so you are not fighting hot water. Then work around the house, doing the radiators that felt cold at the top.
- Hold the cloth under the bleed valve at the top corner.
- Turn the key a quarter turn until you hear a hiss of air.
- Close it the moment water dribbles out, then wipe up.
Check the pressure
On a combi boiler, bleeding several radiators can drop the system pressure. Glance at the gauge and top it up to around one bar with the filling loop if it has fallen too low, or the boiler may cut out.
When bleeding is not enough
If the rooms nearest the boiler roast while the far ones stay cool, the system needs balancing: slightly closing the valves on the hot radiators so more flow reaches the cold ones. It takes patience and a cheap thermometer, but it spreads the heat evenly and is worth a quiet Sunday.