Magnetic Central Heating Filters

About magnetic filters

A magnetic filter is a simple unit that traps any sludge and debris before it can do any damage to your boiler and it’s controls, though there are actually two types of filter, some use magnetic technologies to remove iron oxide particles only, dual–;action units use both magnetic and non-magnetic technologies to remove iron oxides, non–iron sludge and debris in the water, manufacturers claim this type are capable of removing virtually all debris. Some units even have air filtration and separation abilities to remove aerated water from the system. They are easy to install, will help keep your system running at maximum efficiency and maintenance is a simple process, which can be completed within a few minutes as it’s usually only required to be emptied annually, which can be done as part of the annual boiler service.

They’re not bulky units, easily fitted to either horizontal or vertical pipework and are typically fitted to the water return pipe very near to the boiler, they have no moving parts and do not require an electrical supply. They’re available to fit onto either 22 or 28mm pipes and are compatible with most domestic and commercial gas central heating systems.

The fitting of a magnetic filter does not significantly impede the flow of water within the system and they are designed so that the flow of water continues even if the filter becomes full, although they can no longer effectively remove debris from the water when they are full. The filters also provide a convenient point at which to take water samples or add chemical to the water.

Why use them

Good system maintenance, power flushing and adding an inhibitor when a new boiler is fitted, annual boiler servicing and inhibitor checking are known to be the most effective ways of minimising potential heating system sludge problems, but magnetic filters are another way to increase the life and efficiency of your central heating system and further reduce the risk of on-going damage to central heating systems. Especially with the most up-to-date boilers, which may be more prone to blockage due to modern slim-line heat exchanger design.


By ensuring that the water in gas central heating systems remains clean for longer, magnetic filters offer a number of potential benefits:

  • They are quick and easy to install, usually fitted to a pipe close to the boiler
  • The central heating system is more likely to continue operating at a high level of efficiency
  • There should be reduced cold spots in the system (e.g. radiators less likely to become clogged with debris)
  • The lifetime of the central heating system and it’s components is maximised
  • There may be fewer repairs and breakdowns
  • Overall maintenance costs may be reduced
  • Emissions and your carbon footprint may be reduced
  • Homeowners, tenants and businesses may experience lower heating costs
  • A well maintained filter should last for the lifetime of the boiler

When to fit them

There may be benefits in fitting a magnetic filter to any gas central heating system and at any time, but the most appropriate time to fit one is when a new boiler or when any other of the major heating system components are fitted. Magnetic filters really need to be seen as part of a more comprehensive approach to reducing the effect of iron oxides and debris in heating systems, alongside power flushing and a chemical inhibitor being placed within the heating system water.


Magnetic filters are not an inexpensive investment and cost between £80 and £225 per unit (unfitted and excluding VAT), depending on the manufacturer, model chosen and the supplier. However these costs need to balanced against the cost of a new boiler and the potential of using a magnetic filter to extend boiler life, potentially reduced repairs and the possible lowering of ever increasing heating costs for homeowners, tenants and business owners. Often however, it is simply a proactive approach to prevention is better than cure.