Our Tony Hernandez explains and shows you exactly how to clean a MagnaClean filter with simple tools. Follow the video walkthrough below, or read the written step-by-step guide.
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The cleanest, quickest, and stress-free way to get your MagnaClean filter cleaned is to call us out. We clean it as part of a full boiler service, so your entire system gets checked at the same time. We cover North London, West London, Watford, Hertfordshire and Middlesex.
What Is a MagnaClean Filter?
A MagnaClean filter is a magnetic filtration device made by ADEY, fitted to your central heating system — usually on the return pipe near the boiler. Its job is to capture iron oxide particles (commonly called magnetite or sludge) from the water circulating through your radiators and boiler.
Over time, the inside of radiators and pipework corrodes, releasing tiny metal particles into the water. Without a magnetic filter, these particles collect as black sludge inside the boiler's heat exchanger, reducing efficiency and eventually causing breakdowns. The MagnaClean catches these particles before they reach the boiler.
MagnaClean filters are fitted as standard on most new boiler installations in the UK. British Standard BS 7593 recommends that all central heating systems have a magnetic filter fitted and that it is cleaned at every service.
How Does a MagnaClean Work?
Inside the MagnaClean housing is a removable magnetic core — an extremely powerful magnet surrounded by a plastic sleeve. As water flows through the filter, iron oxide particles are attracted to the magnet and held against the sleeve.
The clever part of the design is that the magnet can be removed from the sleeve separately. When you pull the magnet out, the particles lose their magnetic attraction and slide off the sleeve easily under running water. This makes cleaning quick and clean — you don't need to touch the sludge directly.
Signs Your MagnaClean Needs Cleaning
Your MagnaClean should be cleaned at every annual boiler service, but there are signs it may need attention sooner:
- Cold spots on radiators: Particularly cold patches at the bottom of radiators — this indicates sludge is circulating and settling in the system
- Black water when bleeding radiators: The water should be clear. Black or dark brown water means iron oxide is building up faster than the filter can catch it
- Boiler making banging or kettling noises: Sludge deposits on the heat exchanger cause hotspots, which make the water boil locally and create noise
- Boiler losing pressure frequently: While not always caused by sludge, a system full of debris puts more strain on components like the pressure relief valve
- Higher gas bills: A heat exchanger coated in sludge has to work harder to heat water, using more gas for the same output
How to Clean a MagnaClean Filter — Step-by-Step
Tools Needed
You need the MagnaClean key that came with the filter. This key has a larger end for removing the cap and a smaller end for the isolation valves. If you've lost the key, a small adjustable spanner will work.
Have a bucket and some old towels ready — a small amount of water will come out when you open the filter.
Step 1: Turn off the boiler
Switch your boiler off and allow it to cool for a few minutes. You don't want hot water flowing through the filter while you're working on it.
Step 2: Isolate the MagnaClean
On the MagnaClean housing, there are two isolation valves — one at the top and one at the bottom. Use the key or spanner to turn both valves so the handles are crossways (perpendicular) to the pipe. This stops water flowing through the filter.
Step 3: Remove the cap
Use the larger end of the key to unscrew the cap on top of the MagnaClean. Lift it off — the magnetic core assembly will come out with it. Have your bucket underneath to catch any drips.
Step 4: Remove the magnet from the sleeve
You'll see black sludge collected on the outer sleeve. Pull the central magnet out of the sleeve — the sludge will lose its magnetic hold and become easy to wash off.
Step 5: Clean the sleeve under running water
Rinse the outer sleeve under a running tap until the water runs clear. Wipe down the magnet core as well. Check the inside of the filter housing for any large deposits and wipe those out with a cloth.
Step 6: Reassemble
Slide the magnet back into the sleeve. Insert the whole assembly back into the MagnaClean housing — it should slot in at the correct angle without forcing. Screw the cap back on firmly using the key.
Step 7: Open the valves and restart
Turn both isolation valves back so the handles are parallel with the pipe (open position). Check for any leaks around the cap. Switch your boiler back on and check the system pressure — top up via the filling loop if needed.
How Often Should You Clean a MagnaClean Filter?
The MagnaClean filter should be cleaned at least once a year as part of your annual boiler service. Most boiler manufacturers require the magnetic filter to be cleaned during the service to keep the warranty valid.
If your system is older or was not flushed when the boiler was installed, you may find the filter collects sludge more quickly. In the first year after a new boiler installation, it's not unusual for the filter to need cleaning after six months — the new boiler dislodges old deposits that were sitting in the radiators and pipes.
What Happens If You Don't Clean It?
If the MagnaClean filter is left uncleaned, it becomes saturated — it can't hold any more sludge, so particles pass through to the boiler. The consequences include:
- Heat exchanger damage: Sludge coats the inside of the heat exchanger, reducing heat transfer and eventually causing it to fail. A replacement heat exchanger is one of the most expensive boiler repairs
- Pump failure: Iron oxide particles can damage the impeller in the circulation pump, leading to a seized or noisy pump
- Reduced efficiency: A system full of sludge uses more gas to produce the same amount of heat
- Warranty issues: Most boiler manufacturers will not honour a warranty claim if the magnetic filter was not maintained
Don't Have a MagnaClean Filter?
If your boiler doesn't have a magnetic filter, we strongly recommend having one fitted. It's a relatively low-cost addition that protects the most expensive component in your heating system — the boiler itself. We can fit a MagnaClean as a standalone job or as part of a boiler service or power flush.
Frequently Asked Questions
Can I clean a MagnaClean filter myself?
Yes, cleaning a MagnaClean filter is a straightforward DIY task that most homeowners can do. You don't need any specialist tools — just the key that came with the filter (or a small spanner) and a bucket. Follow the step-by-step guide above or watch Tony's video walkthrough. However, the annual boiler service itself must be carried out by a Gas Safe registered engineer.
How do I know if my MagnaClean filter needs cleaning?
The main signs are cold spots at the bottom of radiators, black water when bleeding radiators, boiler making unusual noises (banging or kettling), and higher gas bills. If you notice any of these between annual services, it's worth cleaning the filter early.
Do all new boilers need a MagnaClean filter?
British Standard BS 7593 recommends that a magnetic filter is fitted to all central heating systems. Most boiler manufacturers require a magnetic filter to be fitted and maintained as a condition of the warranty. While not strictly a legal requirement, it's considered best practice by Gas Safe engineers and is fitted as standard on virtually all new boiler installations in the UK.
What is the black sludge in my MagnaClean?
The black sludge is iron oxide, commonly called magnetite. It forms when the water in your central heating system reacts with the steel inside radiators and pipework, causing corrosion. The iron oxide particles circulate with the water and, without a magnetic filter, deposit inside the boiler's heat exchanger and other components. A system inhibitor chemical helps slow this corrosion process and should be topped up at every service.
How long does a MagnaClean filter last?
A MagnaClean filter itself should last the lifetime of the boiler — typically 10 to 15 years or more. The magnet doesn't wear out. The only maintenance required is regular cleaning (at least annually) and occasional replacement of the O-ring seal on the cap, which your engineer will check during a boiler service.
Need your MagnaClean cleaned or fitted? Contact us for a no-obligation quote, or call free on 0800 328 0449. We serve Watford, North London, West London, Hertfordshire and Middlesex.
When did you last service your boiler?
Annual boiler servicing from £110 prevents breakdowns and keeps your warranty valid. Gas, oil, and electric.
