18 June 2026
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Alpesh Trivedi, Director at Magnetic International UK LTD, shares his thoughts on the practical route to compliance, performance, and installer simplicity.
As heat pump adoption accelerates across the UK, particularly in new-build residential developments, attention is increasingly turning to system design, sizing, and controls. However, one critical factor continues to be underestimated: heating water quality.
In a closed-loop systems such as heat pumps and underfloor heating (UFH), water quality plays a direct role in system efficiency, reliability, and long-term performance. Poor water conditions can lead to scale, corrosion, and sludge formation — all of which impact heat transfer and increase the likelihood of component failure.
For installers, this creates both a challenge and an opportunity: how to ensure compliance with manufacturer requirements while delivering systems that perform reliably from day one.
Why water quality is critical in heat pump systems
Heat pumps operate at lower flow temperatures than traditional boilers, which makes them more sensitive to inefficiencies caused by poor water quality. Even minor scaling on a heat exchanger can significantly reduce heat transfer, lowering overall system efficiency and coefficient of performance (COP).
In addition, modern systems often contain a mix of materials — including steel, brass, and aluminium components — which can be vulnerable to corrosion if water chemistry is not properly controlled.
For this reason, most manufacturers of heat pumps, specify strict requirements for system water quality. These typically include limits on:
- Conductivity
- Total hardness
- Chloride and sulphate levels
- pH range
Failure to meet these requirements can result in reduced performance, increased maintenance issues, and in some cases, invalidated warranties.
Meeting industry standards
Alongside manufacturer requirements, installers are expected to follow recognised guidance for closed-loop heating systems. Key references include:
- VDI 2035 – widely adopted for controlling scale and corrosion through limits on hardness and conductivity
- BG29 – covering system cleanliness at commissioning
- BG50 – outlining best practice for system water treatment
These standards are increasingly being specified by consultants and incorporated into project requirements, making water quality compliance a core part of system delivery.
The installer challenge on residential developments
On multi-plot residential developments, maintaining consistent water quality can be particularly difficult. Installers often face:
- Variability in local mains or borehole water quality
- High hardness levels in many regions of the UK
- Tight commissioning schedules
The need for repeatable, scalable & sustainable solutions across multiple properties. Traditional approaches using chemical inhibitors can introduce additional complexity. These typically require accurate dosing, ongoing monitoring, and periodic maintenance. Incorrect dosing or lack of follow-up can lead to inconsistent system protection.
There is also growing awareness of environmental considerations, with some developers and clients seeking to reduce reliance on chemical additives.
A practical alternative: Demineralised water at initial fill
One approach gaining traction is the use of demineralised water during the initial filling of heat pump and UFH systems as well as for refill/ top up, delivered via mobile demineralised filling stations and cartridges.
The term Demineralised water originates from the everyday use, and it is argued that the correct technical term is deionised (desalinated) water, commonly referred to as demineralised water.
Deionised water is produced using a mixed-bed ion exchange resin, which removes both cations and anions, resulting in water with very low ionic content and low electrical conductivity.
By filling the system with demineralised water from the outset, installers can create a clean, controlled water environment that aligns with both manufacturer specifications and industry guidance. Thus, reducing the risks of scale & corrosion in the system and that it operates within the recommended water quality parameters.
Importantly, this approach eliminates the need for chemical additives during commissioning, simplifying the process while still meeting performance requirements.
Case study: Residential heat pump development
A recent residential development in Newcastle upon Tyne provides a practical example of this approach in action.
The project involved the installation of 15 kW heat pump systems across multiple new-build properties, each incorporating underfloor heating.
The installer, Bill Hewison Bespoke Homes Ltd, identified early on that local water conditions posed a risk to system performance. With hard water prevalent in the area, there was a clear need to address potential scale and corrosion issues from the commissioning stage and also for future refill or top up of heating water.
At the same time, the project required a solution that would:
- Meet manufacturer water quality requirements
- Be simple to apply across multiple plots
- Avoid the complexity of chemical dosing
- Support long-term system reliability
Implementation on site
Demineralised filling stations were used for initial filling and cartridges were then installed for refill or top up of both the systems.
The process was straightforward:
- Mobile filling stations were used for initial filling and Cartridges were then installed inline during for refill/ top up of the system
- Water was treated as it entered the system
- No additional dosing or chemical handling was required
The cartridges also provided a practical advantage for installers, with clear visual indicators showing when replacement was needed, making them easy to manage on site. This allowed for a consistent approach to be applied across all properties within the development.
Results and installer benefits
By filling the systems with demineralised water, the installer was able to:
- Achieve water quality in line with manufacturer specifications
- Eliminate scale-forming minerals from the outset
- Reduce conductivity to a controlled level
- Provide stable system conditions at commissioning
From an installer perspective, the benefits were clear:
- Simplified commissioning process
- No need for chemical dosing or balancing
- Reduced risk of installation errors
- Consistent results across multiple plots
For the client and end user, this translated into:
- Lower risk of corrosion and component failure
- Improved system efficiency and performance
- Reduced likelihood of maintenance call-outs
- Protection of manufacturer warranty
Looking ahead: Water quality in a low-temperature future
As the UK transitions towards low temperature heating and electrification, the importance of water quality is only set to increase.
Heat pumps and UFH systems are inherently more sensitive to water conditions than traditional systems, making correct commissioning practices essential.
Demineralised water treatment offers a practical, installer-friendly solution that aligns with:
- Manufacturer requirements
- Industry standards such as VDI 2035, BSRIA BG29
- The need for simple, repeatable processes on site
It also supports a move towards chemical-free system management, which is increasingly relevant in both residential and commercial applications.
Conclusion
For installers working on heat pump and UFH systems, water quality should be considered a fundamental part of system design and commissioning — not an afterthought.
Using demineralised water during initial filling provides a straightforward, compliant, and reliable method of ensuring systems operate as intended from day one.
By removing the variables associated with local water quality and chemical dosing, installers can deliver systems that are:
- Easier to commission
- More efficient in operation
- Less prone to failure
- Fully aligned with manufacturer expectations
In a rapidly evolving heating landscape, getting the basics right — starting with the water — remains one of the most effective ways to ensure long-term system success.
