What is central heating sludge?

Sludge, or magnetite, to give it its proper name, is a black substance in the central heating pipes made up of dissolved and rusted metal.


It forms when the water in the system reacts with the metal in radiators and pipes. Because sludge is heavier than water, it can settle in radiators and pipework and, if left to build up, it can damage the boiler and the system.

Related FAQs

Does my boiler filter need cleaning?

Ask your installer to clean your filter while carrying out your annual boiler service. Read more to find out why this is important...

Do I have to have a magnetic boiler filter installed?

Fitting a filter is considered best practice when installing a new boiler. The installer must carry out the following steps when a new boiler is fitted...

Why should I have a filter fitted?

Many boiler breakdowns occur are due to sludge in the heating system. Find out the many benefits of fitting a magnetic filter & how it can save you money.

Why should I get the water in my central heating system cleaned?

If Boiler breaks down due of sludge in the system, the repair work is not covered by the Boiler warranty & can lead to expensive repair bills. Read more...

Why are my radiators cold?

Not sure why your radiators cold at the top or bottom? Find out the reasons and simple solution to resolve this.

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