WATER TREATMENT
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protecting the metal surfaces within the system. A system filter will capture contaminants already in the system and any debris introduced accidentally.
The impact of temperature and flow-rate differences
There are factors that make heat pumps different from a protection point of view, meaning specific considerations are required. The first and perhaps the most obvious is that the majority of heat pumps operate at much lower flow temperatures, something that is also advocated by the Building Regulations to lower the carbon footprint of homes. These lower temperatures, typically between 35°C and 55°C, means that there is a risk of microbiological contamination as it allows microorganisms such as bacteria and fungi to thrive and multiply. This can lead to biofilms forming on surfaces within the system, causing reductions in system performance as well as accelerated degradation through Microbiologically Influenced Corrosion (MIC). To address this risk, an effective biocide should be added to the heating system alongside the other chemical treatments. This is also mandated in BS7593:2019. Heat pumps also operate at much higher
Keeping heat pumps running smoothly
As heat pumps become more common in new and existing homes, installers must appreciate the similarities and differences to traditional boiler systems and how to protect heat pumps effectively, says David Holley, Fernox technical manager, chemistry
T
he drive for lower carbon emissions has accelerated the adoption of heat pumps, and the upcoming Future Homes
Standard is expected to essentially prevent the use of gas boilers for new homes and major refurbishments. While many heating professionals are now undertaking training and expanding their services into this new area, they also need to fully understand how to protect these systems in the long term. It is firstly important to look at how gas boiler and heat pump systems are the same. Although they generate heat in a different way, heat pumps still use the same water filled central heating pipework, radiators and underfloor heating. Therefore, the system is still vulnerable to corrosion, scale and the damaging effects of circulating debris, and must be protected to ensure longevity and efficiency. The best practice approach to achieve this is the same as with boiler systems – a combination
20 August 2025
Left: David Holley, Fernox technical manager, chemistry at Fernox
flowrates of up to 80 litres per minute. This must be factored in when choosing a system filter. It is important to look for one designed specifically for heat pump systems as the high flowrate can mean some filters will not perform as expected. This is because many of the filters on the market that claim to be suitable for heat pumps rely on magnets to capture the particles. These filters are susceptible to wash-off or lost capture at higher flow rates, meaning contaminants are discharged back into the system water. Filters intended for use with heat pumps will be engineered for efficient capture at high flow rates. For example, the design of the Fernox Sigma HP Filter and it unique ‘Flow Disruptor’ technology creates an area of low flow within the filter body, causing particles to settle towards the base of the filter, even at high flow rates. It is also essential to select a filter that has been designed to optimise the flow of water through it and minimise the pressure losses. This ensures that the system can perform as designed and allow the heat pump to maintain the required COP (Co- efficient of Performance) levels.
Choosing high quality products
of effective water treatment and an in-line system filter, supported by regular servicing and testing of inhibitor levels as outlined in BS 7593:2019. The requirements of this standard have formed part of Part L of the Building Regulations in England since June 2022 and will therefore be familiar to many in the industry.
Combining the two is important. A high-
performance inhibitor will prevent the formation of sludge and limescale build up by chemically
As with all heating systems the quality of the products used on heat pump systems is important. Inhibitor and biocides from reputable manufacturers should always be used and the levels of these should be checked during servicing. It is also vital to select a filter that has been rigorously tested to assess its long-term performance and durability. Despite the similarities between systems with a boiler and a heat pump, it is important to factor in how they differ to ensure heat pumps, and the wider heating system, are adequately protected in the long term.
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