Homeowners Professionals

How to clean a magnetic filter on a boiler

Magnetic filters have been a subject of debate in previous years. Some people think that every heating system should have one installed to keep sludge and rust out of your system.

The fact is, magnetic filters can play an important role in keeping your heating system as clean and debris-free as possible, particularly if you live in a hard water area and your appliances are prone to limescale build ups.

If you do have a magnetic filter installed, you’ll need to keep it clean, otherwise the filter becomes clogged up with dirt which stops the magnet from working as well as it should. So how does a magnetic filter work and how can you clean it?

How does a magnetic filter work?

Any appliance that uses water, from a kettle to a dishwasher, can suffer from limescale and rust, and this includes your heating system. It may be easier to see dirt building up in these appliances, but it’s almost impossible to see the debris that’s in your pipes and radiators. Limescale can also build up in your heating system, particularly if you live in a hard water area, and dirt can enter your radiators via the cold water that comes in through the mains supply.

There are many different metals that can be found within your central heating system. The main three are copper, aluminium and steel. Copper is mainly used for pipes as it’s durable, malleable and lightweight. Aluminium is usually found within the boiler itself because it’s a good conductor and is a relatively cheap material. Steel is the metal that’s most responsible for the black sludge that forms in your pipes and radiators. This is because it corrodes easily when in contact with both water and oxygen.

A magnetic filter works so well because the steel sludge is attracted to the magnet. As this corroded steel debris passes through the system, it gets caught in the filter, allowing the newly cleaned water to continue through your pipes.

Sludge and debris can decrease the efficiency of your home’s heating system and may even leave your radiators with cold spots. If your radiators are only warm at the top, there could be air in your system, or there could be a build up of limescale/sludge/rust.

A magnetic filter is designed to remove this sludge from your system. If your system has lots of rust in it that’s been there a long time, a power flush may need to be performed before the magnetic filter is installed.

As the magnet picks up the dirt, the filter may become blocked, stopping the magnet from working as effectively. This means the filter will need cleaning - so how can you do this yourself?

How to clean a magnetic filter on a boiler

The first thing you should do is turn off the electrical supply to the boiler and lay a dust sheet down just in case any rust gets on your flooring. You should also shut off any isolation valves.

Your magnetic filter should have a simple screw lid, although it may be extra tight for safety reasons. It should also have been supplied with a device that you can use to remove the lid, such as a spanner. Use the spanner to loosen the lid until you can unscrew it using your hands.

When you’ve unscrewed the lid enough to remove it, you’ll find that the magnet and filter are attached to the lid. You’ll see a lot of black dirt all over the filter. The magnet should be easy to slide out of the filter casing. Remove the magnet as that part doesn’t need cleaning.

You should be left with just the filter, which is the only part that needs cleaning. You may want to take it out into the garden as cleaning it could cause a lot of mess. To clean the filter, use a high pressure hose to blast off the rust. If you don’t have a high pressure hose, a standard one will do. Be sure to clean the lid as well as the magnet itself, as this could also have dirt trapped in it.

Once you’ve hosed everything down and it’s free of dirt, you can take the magnet back to the boiler and place it inside its original casing, using your hands to tighten it as much as you can, and then a spanner to fully secure it.

You can now reopen the valve and turn the boiler electrics back on.

The filter should be cleaned about once a year. If you’re unsure about completing this task yourself, you can ask your heating engineer to do the job for you when they’re carrying out your boiler’s annual service. As long as the magnetic filter is easy to access, it shouldn’t make too much of a difference to the time or cost of the service.

Do I need a magnetic filter for my boiler?

There are lots of benefits to having a magnetic filter installed. These include:

  • A more efficient heating system
  • Lower energy bills
  • Longer boiler lifespan

Magnetic filters are completely optional - they aren’t a requirement. However, if you don’t have a magnetic filter, dirt and rust are able to flow around your system, which could put your boiler at risk of becoming damaged and could reduce the efficiency of your radiators.

Reduced efficiency could mean you’re paying more on your energy bills. Failing to remove this dirt could also mean you need to pay for a power flush of your whole system every now and then. In this case, it would be more economical to have a magnetic filter installed to keep your system running in the most efficient way.

Once a magnetic filter is installed, you don’t need to do anything other than clean it occasionally. The filter may need to be replaced over the years, but replacements are reasonably priced.

Your boiler may also maintain its level of efficiency for longer with a magnetic filter in the system, which saves you money on a boiler replacement and may also reduce your carbon footprint.


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