The importance of ensuring high quality system water

The importance of ensuring high quality system water

Richard Crisp, Head of Chemistry at Fernox, looks at the importance of ensuring high quality system water and how this can be achieved, including the latest mandatory requirements and best practice guidance. 

Contamination in the heating system can significantly impact the efficiency, performance and lifespan of the boiler and other key system components. While this has always been a concern, there is now added pressure due to the current cost of living crisis. With the price of energy rising sharply and many homeowners struggling to pay the bills, installers can help customers by ensuring that their system is cleaned, protected and maintained as detailed in the latest version of Part L and BS 7593:2019. This will improve the efficiency of heating systems and prevent premature breakdowns. 

One of the biggest issues is contamination, which comes from a variety of sources. This includes iron oxide sludge caused by the corrosion of steel in the system as well as other metal oxide debris from non-ferrous metals (e.g. copper, brass, aluminium). These contaminants block heating pipes and prevent radiators warming up correctly, causing far more energy to be used. In addition, aluminium components are vulnerable to pitting, which leads to pressure loss and ultimately system failure.  

Limescale is also a serious issue, especially in hard water areas and forms on surfaces within the system, including vital components such as the heat exchanger and pump. British Water estimates that just a 1.6 mm coating of limescale on a heating element can reduce boiler efficiency by up to 12%. 

While contamination is often associated with older heating systems, without the correct protection new installations, including the most efficient ‘A’ rated boilers, can begin to suffer damage and reduced efficiency in a matter of weeks. In fact, the miniaturisation of modern boilers to achieve the compact dimensions that customers demand and to improve boiler efficiency, has meant narrower waterways and channels, which can more easily become blocked by any circulating debris, sludge or scale. 

Efficiency and longevity 

These issues can all be addressed by simply ensuring that the steps outlined in BS 7593:2019, the British Standard for the installation, commissioning and maintenance of domestic heating systems are followed. Since June 2022, the BS 7593:2019 requirements form part of the legal requirements of Part L of the Building Regulations in England. This means that all new homes, or new heating installations in existing properties, must comply with this guidance.  

Part L now requires the system to be cleaned fully, dosed with a high-quality inhibitor to prevent the formation of sludge and limescale, and the boiler further protected from circulating debris with an inline system filter. This must then be maintained with regular servicing and maintenance, including tests of the system water to check inhibitor levels. 


Of course, what is required for each system will depend on its condition and how well it has been maintained in the past. Where a system is contaminated, the first step will be cleaning. A high quality chemical cleaning solution will effectively remove sludge, scale and debris. For heavily contaminated installations, it may also be advisable to carry out a powerflush to ensure the system is cleaned thoroughly. New systems should also be cleaned as part of the mandatory Part L prescribed commissioning process to remove any installation debris and other contaminants. 

Guard and Protect 

Once the system is clean, it is important to protect it from future contamination. Dosing the system with a high-quality inhibitor will prevent the formation of sludge and limescale build up by chemically protecting the metal surfaces within the system. Some inhibitors, such as Fernox Protector F1, feature enhanced pH buffering to ensure the pH level remains between 6.5 and 8.5, which is the optimum range to prevent corrosion in mixed metal systems.  

An inline system filter should also be fitted – and this is now a mandatory requirement of Part L of the Building Regulations for England. An inline filter will protect and guard the boiler and heating system by capturing sludge and debris for simple removal. Choosing a high quality filter that is designed to capture both metallic and non-metallic debris will ensure more effective protection of the system. This will help deliver both improved energy performance and system longevity. For example, the Fernox TF1 Sigma Filter and TF1 Omega Filter achieve this with a unique combination of a powerful neodymium magnet and Hydronic Particle Separation (HPS) technology. 

In addition, for systems with a lower flow temperature, such as those with a heat pump, microbiological protection is also required. At these temperatures, typically between 35°C – 55°C, microorganisms such as bacteria and fungi will thrive. This not only poses a health risk but can also cause accelerated degradation through Microbiologically Influenced Corrosion (MIC) and reductions in system performance due to the formation of biofilms. On these lower temperature systems, a biocide should be added to the heating system water. The biocide will kill the microbes by altering the cell wall permeability and interfering with biological processes, destroying the cell as a result.  


It is essential for a heating system to be serviced and maintained regularly, at least every 12 months, to ensure it remains contaminant free and continues to function as efficiently as possible. This should include cleaning of the filter to remove the captured sludge and debris as well as a check of the inhibitor levels using an on-site test, which is required by Part L. The Fernox Express Inhibitor Test, for example, provides a quick and easy method of checking the concentrations whilst on site, with a simple dip test on a sample of the water. If the levels are not sufficient, inhibitor can be added, and the system retested to check the concentration with no return visit needed. 

In addition, every five years the system should be either re-dosed with inhibitor or a full laboratory analysis of the system water conducted. This can be completed relatively simply with test kits such as the Fernox Water Quality Test. Installers simply collect a sample of the system water and send it to the laboratory for a full analysis and report of key system water parameters. With the Fernox kit, results are returned within 48 hours and all samples and results can be managed through an intuitive mobile app. 

Ensuring a heating system is clean and protected can make a significant difference to its efficiency and longevity – something that is now essential for many homeowners. Prevention is often far easier than a cure so effective annual maintenance and testing is crucial. Comprehensive cleaning, protection and testing of the system is also now a mandatory requirement of Part L compliance. 

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