System Filter

The Importance Of System Filters

Before you buy a Filter…

System Protectors, or Magnetic Filters, are a fantastic technology available to help protect your boiler from corrosion and damaged caused by sludge in your system; extending your boiler’s lifespan and preventing expensive repair bills. They should however, be used as the last line of defense and do not perform miracles.

Whether you are having a new boiler installation or trying to protect your existing system the first thing you should check is that your system water is clean and that it contains Inhibitor (also known by the trade name Fernox).

You can check this by bleeding a radiator into a container and looking at the colour of your system water, if it is dirty you need to get an engineer in to quote for a flush. I will cover different types of flushing in a future post.

Testing for inhibitor is not as simple as some sites like to make out. You can get test kits, these are relatively cheap, however only test for specific brands. For example, if you test with a Fernox test kit it will say “no Fernox F1 Present” however you may have “Sentinel Inhibitor” installed. When in doubt you can always drain the system and add more.

Another common misunderstanding is that Inhibitor is a magic substance that eats dirt; this is incorrect. You must first flush out any dirt then add inhibitor that will make sure your water stays clean. If you have a really dirty system you can add as much inhibitor as you want it won’t make a scrap of difference.

Now that’s out of the way

Now your system has been flushed and you have inhibitor installed… so why do you need a system filter?

I challenge the best of heating engineers to guarantee to remove 100% of sludge and debris from any heating system. A small amount of dirt will always remain and if it gets into the boiler can cause problems.

Your system filter will collect this dirt before it goes into your new shiny boiler. The sludge in your heating system is actually “Iron Oxide” and will cling to the high powered magnet inside your filter and stop it from entering the boiler. Then every year during your gas service your engineer should take this apart and clean it thoroughly.


You’ve just had brand new radiators and pipework

So you’ve just had a complete brand new heating system. Your engineer has flushed, cleaned and protected your system. You can practically drink the water (don’t drink your radiator water). So why would you need a System Protector?

Two reasons:

  1. Some manufacturers, such as Worcester-Bosch and Vaillant (the only two boiler manufacturers I would recommend) now offer increased Guarantees on their product if you purchase their system filter. These cost roughly £30-£40 more than the standard filters on the market but are a solid investment when you take into account the extra Peace-of-mind.
  2. Your system may be clean now, and as long as you have inhibitor in your system it will stay clean. However, in 5 years’ time when you finally get round to getting that spare room decorated and your decorator drains your system to remove your radiators… Do you really think he will pay £20 for some more inhibitor?

Ihave seen brand new heating system water turn orange in as little as 2 weeks! And before you know it your lovely new system can start forming sludge. That system filter will now collect as much of this as possible to try and protect your boiler.

It will also raise alarm bells when your service engineer comes to clean the filter on your service and notices sludge, he can now drain and re-fill your system will inhibitor and save you money on hefty repair bills. #WIN

Which System Protector should I get?

Like most products today there is so much choice! When it comes to a system filters there are only a few things to take into account:

  • Will it increase my boiler’s Guarantee (try to get boiler brand filter for the extra peace of mind)
  • Is it easy to clean? (If your filter isn’t easy to clean chances are your service engineer won’t clean it! Don’t give them an excuse, get a system protector that’s super simple)
  • Is it big enough for your system? (most manufacturers make 3 sizes of filter, small medium and large, ask your engineer how many radiator your protector can cope with and make sure it’s up to the task)
  • Cost (system filters can vary in price, some costing double than others, but from my experience you do get what you pay for)
Worcester-Bosch System Protector Adey Magnaclean Fernox TF1 BoilerMag SpiroTec
Increased Guarantee Yes No No No No
Easy to clean Very easy Very easy Seal will need to be changed on every clean Easy but BULKY No removable incert or isolation vales. Near impossible
Various Sizes M L S M L S M M M
Cost £££ ££ ££ £ £
*The chart above is compiled by my personal opinion and feedback from my service engineers.


In summary my advice would be to always have a system protector fitted when you have a new boiler. The £60 – £100 extra you will spend will pay itself off in the long run. If you have an older system it is debatable whether to wait and have a protector installed when you upgrade to a new boiler as this would be easier and cheaper on labor/ installation.

My personal preference would be an Adey Magnaclean. They are simple to clean, reliable and reasonably unobtrusive. The alternative for a new Worcester-Bosch boiler would be their own protector that is also made by Adey and shares and identical design but can increase the boiler’s guarantee to as much as 10 Years.

If in doubt ask your engineer or for more information please contact us on 01782 811102.

Affordable Luxury for the UK's most reliable boilers.