This month, Mimi from Hammersmith asks…

Dear Samuele,

I’ve always done my best to keep my plumbing and heating well maintained including regularly bleeding my radiators and checking boiler pressure.

However, in recent weeks I’ve noticed that the bottom of my radiator remains cold when the heating is on. Can you tell me what’s causing it?

Yours sincerely,

Mimi

Ciao, Mimi. And grazie mille for your question!

If a radiator is cold at the bottom but warm at the top, bleeding it usually won’t solve the issue. More often than not, it’s caused by a build-up of sludge, rust, and debris inside the radiator over time.

This sludge settles at the bottom and restricts the flow of hot water, meaning the radiator can’t heat properly. It’s especially common in older heating systems.

In some cases, the radiator may need flushing through. If the problem is affecting multiple radiators, it could indicate the whole heating system would benefit from a power flush or magnetic filter installation.

Left untreated, sludge can reduce efficiency, increase heating bills, and place extra strain on your boiler.

Worst case scenario: if the power flushing doesn’t make it significantly better, a complete radiator replacement might be required.

Hope that helps.

Samuele

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