Does my boiler need a system filter?

Having system filters fitted to modern gas boilers have become more and more popular as a means of increasing the lifespan and improving efficiency of boilers. Once seen as a novelty item, the system filter is now seen as an essential part of any new boiler/central heating system and even as an addition to an existing system. Coming in all makes, shapes and sizes; system filters serve a real purpose when installed correctly as part of a heating system.  The majority of boiler installation companies nowadays will provide a system filter with every install as standard.

What is a system filter?

A system filter is a metal/plastic component which is connected on the return pipework of a central heating system. Inside, it has a very powerful magnet which grabs any sludge that builds up in the system over time. This sludge is made up of rust particles from the inside of pipes and radiators that have corroded over time.

Boiler system filter

The idea of a system filter is that it is to be located on the return pipework of a heating system, as close to the boiler as possible. A system filter will catch the sludge before it enters the boiler, preventing it from getting into the boiler components, therefore prolonging the life of the boiler. The filter can be cleaned out during your annual boiler service by a qualified heating industry engineer.

Do I need a system filter?

There is no definitive answer as to whether you should have a system filter installed as part of your system but the visible collection of waste material that is collected each year is quite surprising, even in fairly new heating systems.  Would you rather have that sludge removed or left to circulate the system and make its way into your boiler components?

So, why do we have sludge in our central heating systems? Well, sludge will accumulate in a heating system as the system is made up of various components and dissimilar metals. The metals can ever so slightly corrode and mix together with the chemicals in the system, forming a sludge. This sludge also forms at the bottom of your radiators, which is why on particularly old systems with old radiators, the bottom of the radiators might not be as hot as the top. A sludge mound can settle at the bottom of the radiator stopping the hot water produced by your boiler from heating it up. There are a few ways to help remove this, one being a power flush but this procedure can be quite costly. It’s also not recommended for very old heating systems as the process is quite vigorous and can be detrimental to the health of old pipes.

How much do they cost?

Typically, system filters with installation from a qualified heating industry engineer can cost anywhere between £150 – £250. This is dependent on the brand and the engineer.  There are multiple filters on the market today, some more aesthetically pleasing than others but all serving the same purpose.


In a nutshell, a system filter is designed to prolong the life of your boiler and help your heating system run more efficiently. The recognition of the practicality of system filters is now as such that boiler manufacturers such as Worcester-Bosch have offered a 1 year extension on the boiler guarantee when their own system filter is installed alongside their boiler. If one of the world’s leading boiler manufacturers is willing to offer an extra year guarantee for the presence of one of these devices then that’s got to count for something, right?

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