What Can I Do If My Radiator Is Cold At The Bottom?

We all know heat rises, so a radiator that’s cooler at the bottom than the top may not worry you too much. But it could indicate a problem. So what can you do if your radiator is cold at the bottom…

My Radiator is Cold at the Bottom

If your radiators are colder at the bottom than the top, this means the flow of hot water is being restricted so it’s not reaching the whole radiator. The culprit is often a build-up of sludge and grime.

As soon as the sludge is enough to block off flow channels inside the radiator, hot water cannot heat through. If several channels get blocked, the whole of the bottom of the radiator will get no hot water.

Fixing radiators that are cold at the bottom

There are three ways to solve this problem: chemical, cleaning or a power flush.

Adding cleaner

A chemical can be used to clean up the sludge – you add it to the system, let it run for an hour or so, then flush it out. In severe cases, a cleaner can be left in for a week, but it eventually needs to be removed fresh water added. This is best left to a professional central heating engineer.

Cleaning a single radiator

Removing and cleaning a radiator is not too hard for a DIYer.

1. Isolate the radiator: if it has thermostatic radiator valve (TRV), turn it down to zero. At the other end is a “lockshield valve”, which is usually covered with a plastic cap. Close it with a spanner, but note how much you turn it.
2. Put an old towel underneath the nuts, and place a bowl on the towel.
3. Turn the radiator nuts slightly with a spanner. A small amount of water may drip out.
4. Using a radiator key, open up the bleed valve to let air in, and water will come out near the loosened nuts.
5. Once the water stops flowing, undo the valves fully and remove the radiator from its brackets.
6. Take the radiator outside, attach a hose to one end and blast water through until it flows clean.
7. Hang the radiator back on the brackets, re-attach the pipes with the nuts and turn the valves back to their original positions at. Water will come in, so be ready with the bleed key and close the valve as soon as water comes from it.

Power flush

A power flush is the same as the operation above, without removing the radiators – another job for the professionals.

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