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What Are Magnetic Filters?

Installer working on Vaillant ecoTEC plus boiler

What is a magnetic filter?

A magnetic filter is a device that collects magnetic debris within a heating system. Rust and corrosion can form in pipes over time, and the subsequent debris will peel off and combines with other debris to form a sludge-like substance. This sludge can cause blockages and other issues on the system, causing it to work less efficiently and potentially causing breakdowns.

A magnetic filter will attract the corroded metals to stop them from building up. The filter allows water to continue flowing through the system as normal and can keep a system as cost-efficient as possible for longer.

Installer checking radiator in living room

Do I need a magnetic filter?

There are several signs that suggest a magnetic filter would be beneficial for your system’s efficiency. These include:

  • Cold spots on a radiator. If your radiators stay cool at the top but become warmer at the bottom, it is likely that sludge is blocking the flow of water in the radiator.
  • Strange boiler noises, such as gurgling or banging, are another sign that sludge has built up in the system.
  • Regular leaks can also point to a sludge problem.
  • Issues relating to temperature, for example where the hot water or heating may not be hot enough. The system water quality can contribute towards this.

The longer these issues are left unresolved, the more damage this can potentially inflict on your boiler. Not only can this result in higher energy bills, but it may also require expensive boiler repairs, or even a new boiler.

A magnetic filter will help combat these issues. Nevertheless, significant build-up cannot be solved with just a magnetic filter. In severe cases a system cleanse may be necessary, which must be carried out by a qualified heating engineer.

How do I install a magnetic filter?

Magnetic filters are usually fitted when a boiler is first installed however they can be added to an existing system by a Gas Safe registered engineer, if there is sufficient space. They are installed on the boiler return pipe (the pipe that returns water to the boiler once it has travelled around the heating system).

How do I clean a magnetic filter?

Regular servicing is necessary to ensure that the magnetic filter is working properly. It is recommended that magnetic filters are cleaned every year to remove the debris it has caught and to keep it in good working order. Your heating engineer will be able to do this for you during your annual boiler service.

Are magnetic filters worthwhile?

Without a magnetic filter, it is almost inevitable that sludge will build up in a home’s heating system and create issues. A magnetic filter will help combat this problem and keep energy bills low for as long as possible, making it a cost-effective investment. However, if your system has already been treated with a corrosion inhibitor it may not be necessary to install a magnetic filter as well.

An added benefit of installing a magnetic filter is that it can sometimes lead to longer boiler warranties. Vaillant offers an extended 10-year warranty on some of our boilers when installed with a boiler protection kit, which includes a magnetic filter. This is only possible if your new boiler and protection kit is installed by a Vaillant Advance installer, so if you're interested you can get in touch with one to discuss your options.


  • A magnetic filter is a device that collects debris build-up in a heating system.
  • Cold radiators, strange boiler noises and even boiler leaks can be signs of sludge build up.
  • Magnetic filters are usually fitted during the boiler installation, but can also be fitted onto an existing system.
  • A qualified heating engineer should clean the filter once a year to keep it in top condition.
  • Magnetic filters can lower energy bills and avoid costly repairs, making it a worthwhile investment, especially if it extends the warranty period on the boiler.