Radiators warm at the bottom but cold at the top in your Birmingham home? That is usually air. How to bleed a radiator safely, and what it means if the air keeps coming back.
Trapped air sits at the top of the radiator and stops hot water filling it.
Heating off, radiators cool, a quarter turn on the bleed valve with a cloth ready.
Bleeding lowers the system pressure, and a combi may need topping up.
A sign of a small leak, a pump problem or corrosion inside the system.
A different fault. A clean or power flush rather than bleeding.
Protects the inside of radiators and pipes from the corrosion that makes gas and sludge.
Usually once a year when the heating goes back on, or whenever one is cold at the top.
Yes. Bleed with the heating off and the radiators cool, both for safety and so air is not drawn in.
Top it up using the filling loop as the boiler manual shows, to around 1 to 1.5 bar with the heating cold.
Something is letting air in or producing gas, often corrosion inside the system. It needs looking at.
Yes, with a chemical clean or a power flush, then inhibitor and a magnetic filter to keep it clean.
Ask to see the Gas Safe ID card when they arrive. The back lists exactly which appliances that engineer is qualified to work on, and the number can be checked on the Gas Safe Register.
A radiator that is warm at the bottom and cold across the top almost always has air trapped in it. Air rises to the top of the radiator and sits there, so hot water cannot fill the whole panel. It is one of the most common heating complaints in Birmingham when the heating goes on for the first time each autumn, after months of sitting still.
Bleeding the radiator lets the air out. With the heating switched off and the radiators cool, use a radiator key on the small valve at the top corner, turn it a quarter turn with a cloth underneath, and let the hissing air out until water starts to appear. Close it again. Then check the boiler pressure, because letting air out also lets pressure out, and a combi may need topping up afterwards.
If the air comes back every week or two, something is letting it in or making it. A small leak somewhere on the system can draw air in as the system cools. A pump that is set up wrongly can pull air through. And in older systems, the corrosion inside steel radiators produces hydrogen gas, which collects at the top in exactly the same way, and that is a sign the system needs cleaning and protecting with inhibitor.
If the radiator is the other way round, cold at the bottom and warm at the top, it is not air at all. That is sludge, and bleeding will not help. A clean or a power flush is the answer.
If you smell gas, leave the house, do not touch switches and ring the National Gas Emergency line on 0800 111 999 from outside.
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