Published in May 2019 the new BS 7593:2019 provides clear guidance on the preparation, commissioning and maintenance of domestic central heating and cooling water systems.

Here, Francine Wickham, Global Marketing Director at Fernox takes a look at the revised code of practice and explores the latest product innovations available, to make it easy for installers to comply. For many years the chemical water treatment industry has been championing life-long protection of central heating systems, to improve energy efficiency, minimise fuel wastage and ensure system longevity – and as a leading member of the BEAMA water treatment committee, Fernox has played an active role in the development of the latest revisions to  BS 7593:2019, which aims to clarify and promote best practice, for the lifetime of the system.  

Fernox supports the new legislation through its Research and Development programme, as the company recognises the crucial role product innovation and application must play in encouraging the wide-spread adoption of new practices and processes – where ease of use and reliable product performance is key. 

The latest code of practice covers five key areas – clean, guard, protect, maintain and test – to not only ensure compliance but to also ensure systems are performing at their optimum level.


Before an existing central heating system is dosed with chemical water treatment or a filter is installed, it is vital that it is cleaned to remove any existing sludge or debris build-up. For best results, installers should use a recognised cleaning method such as powerflushing, mains pressure or gravity cleaning.

It is also important that systems are cleaned before the boiler is installed or when a new boiler has been isolated from the rest of the system. This will prevent any existing sludge or debris within the system reaching and depositing in the boiler and causing lasting damage.

2. Guard

Once a central heating system is cleaned, it is key to make sure that sludge and debris does not build-up once more. The new BS 7593:2019 code of practice states that, in order to do this, an in-line filter should be permanently installed to provide continued protection and maintain system efficiency.

It is important that the chosen filter can effectively capture and contain both magnetic and non-magnetic debris to keep the system as clean as possible. Filters manufactured by leading water treatment specialists, that utilise a powerful neodymium magnet and other technology such as Hydronic Particle Separation (HPS) are better able to achieve this – and can therefore deliver optimum results.

For ease of install, it is important to consider whether the filter can be installed in a variety of orientations, such as horizontal, vertical, or with the capability of being installed up to 45° orientation in order to fit small confined spaces, such as the Fernox TF1 Filter range.

3. Protect

To protect a central heating system from corrosion, scale, microbial fouling for low temperature heating systems, installers should dose the system with the correct quantity of chemical water treatment products. This should include Protectors to protect against harmful sludge and debris build-up. It is best to choose products from a reputable manufacturer, to guarantee that the chemicals will continue to protect the system effectively.

It is also important that systems are dosed correctly – the Fernox ‘F’ range of chemicals, for example, have recently been re-formulated to include more active ingredients; and can now treat systems up to 130 litres, 16 radiators, or underfloor systems up to 250m2. This will significantly lower the chance of under dosing, to cover 97% of UK homes.

For low temperature or underfloor heating circuits, which are at risk from bacterial contamination and fungus, specialist biocides are available. Fernox Biocide F7, for example, protects against bacterial slimes, algae and biofilms forming, which can cause blockages, inefficiencies and ultimately breakdowns.

System Filters can directly protect the boiler to ensure that any circulating debris that is present within the system does not reach vulnerable components such as pumps or heat exchangers.

For hard water areas with a ppm of 200 and above, a scale reducer should be fitted to mitigate the effects of limescale. Electrolytic Scale Reducers offer whole house protection whilst Magnetic Scale reducers are designed to be fitted next to the boiler for single appliance protection.

4. Maintain

BS 7593:2019 states that servicing of in-line filters is recommended as part of the re-commissioning process, ideally as part of the annual boiler service and according to the manufacturer’s instructions – to remove any sludge or debris that has been captured. This will ensure that the filter continues to work at its best, removing contaminants from the system.

Fernox TF1 Sigma and TF1 Omega filters are great examples of innovative, non-lidded filters that enable fast, mess-free maintenance and cleaning. With this unique sealed filter design, sheathed magnet and drain valve features, there is no need to dismantle the filter during the cleaning process – this also means that there are no additional, replacement parts required, such as replacement ‘O’ rings. Time on site cleaning the system is reduced and there are no ongoing servicing costs. These sealed, lid-less filters can be cleaned simply by turning off the system, opening the drain valve and removing the magnet from the sheath – dirt will then flow out, cleaning the filter without the installer having to touch or clean a dirty magnet.


To ensure full system protection, inhibitor levels should be checked throughout its life cycle. This can be achieved with a full laboratory analysis of the system water. Simple test kits are available – these require a sample of the water to be taken and sent off to a laboratory for testing. Results can then be accessed easily through apps such as the Fernox Water Quality Test App, which provide all test results in a clear, easy to access format with regular status updates.

In order to meet the requirements of BS 7593:2019, it is vital that installers look to specialist manufacturers who demonstrate an understanding of the on-site challenges, with an extensive product portfolio that offers a solution for every application – and ensures compliance on every project.