How to clean a magnetic filter and give your heating a boost
One of the easy but necessary jobs I do before winter is to service my heating system. Keeping it in top condition means I can expect warm water and a warm house through the cold weather without having any issues.
Part of that serving includes cleaning out the magnetic filter which is fitted and helps to protect the boiler and the radiators from blocking up with sludge.
Follow the simple guide below to clean the magnetic filter and give your heating a boost:
Find the magnetic filter trap, turn off the boiler and isolate the heating system, remove the magnet filter lid, check the magnet assembly, clean off the black sludge in a bucket, check the filter lid and ‘O’ ring seals, refit the Magnet assembly, open the Isolation valves and check for leaks.
Cleaning out the magnetic filter is a really easy job and quick to do, but it pays dividends in the long run as keeping the filler clean will keep your boiler clean and healthy for many years saving you on repair cost and help avoid a cold house, read my detailed guide for more tips on how to do it, and check out the video at the end of the guide.
Locate the magnetic trap
Locate the magnetic trap, they are usually installed in the return flow pipework, between the last radiator and the boiler. They are often hidden inside cupboards or behind covers to make the plumbing look tidy.
Make sure you have access to the magnetic filter and the lid, you will need room to fit and turn the spanner, if the unit is fitted inside a cupboard, clear away any items that are stored near it to give yourself room to work.
Turn off the boiler and isolate the heating system
Turn off/Isolate the boiler and make sure the heating system is cool. Most modern boilers will have an on/off switch located on the front panel or an isolating switch.
Check that the heating system is not hot, carefully hold your hand near a pipe or radiator, if you can touch it and hold your hand against it without any discomfort you should be ok, but take care as the water inside the system can still be hot.
Put down an old cloth or towel underneath the magnetic filter to catch any spills, I often use a small ice cream tub to catch any dirty water or drips that can spill out when opening the magnet trap lid.
In most cases if the magnetic filter has been installed correctly there will be 2 shut-off valves fitted to the magnetic filter body and the connecting pipework, these are to isolate the filter body from the heating flow, these valves need to be closed off to allow access to the lid without the heating system leaking.
Normal operation of the isolating valve will mean that turning the valve knob to be perpendicular to the centerline of the pipe closes the valve, and when the isolation valve is in line with the heating pipework the valve is open.
On some makes of magnetic filter, there is a drain at the bottom to allow the unit to be emptied once isolated from the heating system, open the drain carefully and allow any dirty water to drain into the ice cream tub.
If your unit does not have a drain point then this step can be ignored.
Remove the Magnet filter lid
Plumbing magnet filters have a lid at the top which is removed using a spanner that is supplied when the unit is fitted if you don’t have one you can order a replacement or use a strap spanner,
Using the right size spanner loosen the lid is important and I would recommend buying one as they are not expensive and make the job much easier to complete.
If the lid is tight and won’t loosen easily then gently tap the spanner with a hammer to free it off.
With the lid now lose allow any remaining dirty water to drain away if there is a drain point fitted to your unit
On units that don’t have a drain like the MagnaClean I have the steps for draining the water out are not required. And you can often remove the lid and magnet assembly without drawing the water, this can be a benefit as means there will be less air in the system when you reassemble the magnetic filter.
To remove the magnetic assembly from the filter, undo the lid by turning it anti-clockwise and carefully lift out the magnet, then turn the lid upside down and use it to catch any drips.
I always have some blue paper towels handy for plumbing jobs like this to wipe up any mess or spills and covering the magnet assembly with a paper towel and place it in an old bucket or sink will avoid any further mess.
Check the magnet assembly
Have a look at the magnet assembly, and check the condition of the magnet and how much sludge and swarf has been collected and removed from your heating system.
The black material is made up of metallic particles that have been pulled out of the water flowing around the heating system and the magnet filter pulls the metal out of the flow and stops it from blocking the pipes, pumps, and radiators, allowing them to work efficiently.
Lots of metal could indicate that the heating system needs a flush or that a radiator is corroding and may need further attention.
Clean off the black sludge in a bucket of water
Remove the outer protective sleeve from the magnet assembly, some units have a locking mechanism which should twist to loosen the outer protective cover, it’s worth checking the manufacturer instructions for this.
Using an old bucket or a sink, clean off the metal particles and black sludge from the magnet sleeve, flush it off with clean water and a soft brush, I use an old washing-up brush because the bristles work well and they can be easily cleaned afterward.
After you have cleaned off the magnet cover, give it a good wipe down with a dry cloth or some paper, then clean the rest of the magnet assembly with a clean dry cloth or some paper towels to remove any traces of dirt or the black metal particles that form the sludge found on the filter.
Check the filter lid and ‘O’ ring seals
Give the magnet filter lid a good clean to remove any dust and dirt, then remove the ‘O’ ring seal that is fitted inside the lid, use a small flat head screwdriver to carefully lever the seal out of the seal groove.
Wipe the O ring seal clean and check it for wear or damage, O rings can split, get caught on the threads or the lid, and have nicks or flat spots which will stop them from sealing properly against the inside faces of the filler or the lid.
If you see any damage I recommend you replace the seal as even a small nick can create problems and turn a simple job into a major one.
If you are going to regularly clean your magnetic filter it’s a good idea to buy a spare seal kit in case you need to replace the O ring in the lid or any other part of the filter.
Refit the Magnet Assembly in to the Filter
Once all the parts of the magnet assembly have been cleaned and the filter body has been wiped down, the magnetic filter can be put back together.
Make sure to close off the drain plug if it was opened, otherwise, the heating system will leak out when you open the isolation valves.
With the new O ring in place, refit the filter lid, take care that the lid fits properly and is level to start the thread, to avoid stripping the threads or catching the O ring seal, both of which could cause damage and result in the unit leaking
Once you have screwed the lid down as far as you can by hand, use the special spanner to tighten it down, make sure you use the correct size spanner otherwise it may slip and damage the lid.
Sometimes tapping the spanner round with a mallet is required to get the lid tight and fully sealed.
Open the Isolation valves and check for leaks
Before you open the heating system double-check the drain valve is closed and the lid of the magnetic filter is tight.
Slowly open the filter isolating valves to allow a gentle flow of water from the heating system to refill the magnetic filter body
Whilst you fill the valve keep checking for any leaks, keep the ice cream tub, and a cloth underneath the magnetic filter to make sure any leaks are caught and the water does not go anywhere.
Once you are sure there are no leaks from the lid of valves then you can fully open the isolating valves to allow the heating system through the magnet trap.
I tend to leave the magnetic filter for 10 minutes with the boiler and heating off to double-check there are no leaks from the lid or the drain valves.
Turn on the Boiler and test the heating
After 10 minutes if there are no signs of a leak, turn the boiler back on, make sure you follow the boiler manufacturers instructions for this, which can usually be found in the user guide or handbook, then allow the heating to run for about an hour, this makes sure everything is warm.
Whilst the heating is running check the magnetic filter for leaks every 15 minutes, if the lid is leaking use the filter spanner to tighten it down further.
Once the system is running and there are no leaks from the magnetic filter you can wipe up with the cloth and clear away the ice cream tub and your tools and put away your tools.
Now that the magnetic filter for your heating system has been cleaned and serviced it will help give your heat system the best performance and prevent any blockages and keep the pump and valves clean and working for much longer.
How often should you clean the magnetic filter?
Most heating systems need to be serviced regularly to keep them in top working order, I have my boiler checked by a qualified plumber every year before the winter.
As part of this regular service, I also clean out and service the magnetic filter to make sure it functions properly, and helps keep the boiler running smoothly and free of debris.
The manufacturers of class-leading ‘Magnaclean’ filters recommend the following:
‘A MagnaClean Professional has been designed to retain, on average, a year’s build-up of debris. Therefore, servicing is required once a year with the annual boiler service. If the system has a heavy debris build-up, or a power-flush was not carried out, we recommend cleaning the filter at appropriate intervals during the first year of installation and annually thereafter.’
How long do Magnetic Filters last?
Magnetic filters for heating systems do not have any moving parts and are quite simple units, which means they have nothing to really wear out.
Most suppliers suggest that so long as the filter is regularly cleaned and serviced it should last as long as the lifetime of the boiler, which is typically 10 years.
Good brands such as the MagnaClean come with a 2-year warranty for peace of mind.
I have a pacemaker fitted, will the magnetic filter affect it?
If you have a pacemaker fitted, as with any magnetic product, caution must be used when handling a magnetic filter. They are relatively low powered magnets, and with the unit assembled will typically have a smaller magnetic field than a fridge magnet.
However, magnetic central heating filters are a magnetic device and should be handled accordingly.
If you are uncertain about the effects then leave the unit alone and call a professional plumber.
Here’s the ADEY video showing a guide to cleaning a Magnetic filter.
This article was written by: Richard Quinton – The DIY Help Desk Owner, Engineer & technical specialist.
Richard is one of the key partners in The DIY Help Desk team. He is a qualified Engineer, writer, and publisher, educated to Master’s level. He is a keen advocate of DIY and home improvements.
Richard enjoys helping others to learn new skills and reach their goals and believes that passing his knowledge and experience on through his writing is an effective way to positively impact the lifestyles and well-being of others on a larger scale.