HHIC and the HPA have published updated guidance on water treatment and how to maintain a healthy and efficient domestic heating and hot water system.
The Heating and Hotwater Industry Council (HHIC) and Heat Pump Association (HPA) have published updated guidance to help heating and plumbing professionals maintain safe, efficient and long-lasting heating and hot water systems in UK homes.
The document, ‘Maintaining a Healthy & Efficient Domestic Heating & Hot Water System’, was developed to offer advice on best practice across both boiler and low-carbon heating systems.
The guidance outlines best practice procedures for cleaning, flushing, protecting and maintaining domestic heating systems. It also provides clarity on compliance with BS 7593:2019+A1:2024 and the new standard BS 9593:2024 for assessing the performance of chemical inhibitors, ensuring systems operate efficiently and reliably, whether they are powered by a boiler, heat pump or hybrid setup. The document also discusses alternative approaches to corrosion protection of heating systems.
Maintaining good system water quality supports appliance longevity and performance and also underpins the UK’s efforts to decarbonise and transition to cleaner energy.
Stewart Clements, Director at HHIC, says: “Heating engineers play a vital role in keeping homes safe, warm and energy efficient. This updated guidance supports them with clear, practical steps for maintaining system health, helping to ensure that every installation delivers optimal performance and aligns with current regulations and standards. Our collaboration with the HPA has ensured that this advice applies equally to both boiler and heat pump systems as the market evolves.”
British Standards
The new BS 9593:2024 – Assessment for the performance of chemical inhibitors for use in domestic central heating and cooling water systems – Test method has replaced the NSF Industry test standard (formerly known as BuildCert) within the Chemical Inhibitor Approval Scheme (CIAS) for Domestic Hot Water Central Heating Systems. This provides installers and consumers with the confidence and protection of a British Standard that will be managed by BSi.
Performance of chemical inhibitor is tested in three stages:
- To determine the corrosion rate and pitting of standard metal coupons in inhibitor solutions at the manufacturer’s recommended strength.
- To determine the tendency of the inhibited solution to form scale.
- An evaluation of the effect of the inhibitor on non-metallic materials.
The guidance says protecting a heating system against corrosion with an alternative method to that outlined in the Building Regulations should be considered with caution, according to the new guidance. If something goes wrong with the system after a different approach is used, installers must make sure the method is supported in the UK by the original equipment manufacturer, as warranties can be linked to sufficient concentration of inhibitor.
A step-by-step approach
Changes to BS 7593 laid out requirements to test the water throughout the life of the heating system. This commences with commissioning and testing the water to ensure the system water is clean, and then adding adequate top up levels of inhibitor during the annual heating appliance service.
In addition to an annual system water check, the whole system should either be re-dosed at five-year intervals, or a lab test carried out to assess the quality of the water. It is good practice that any new appliance should not be connected until the system has been cleaned. Appliance manufacturer and critical system component instructions should also be checked with regard to isolation of the appliance or components if they are likely to be sensitive to different flushing and cleaning products and techniques.
To comply with BS 7593:2019 +A1:2024 the following steps are a best practice approach to water treatment.
Step 1 Cleaning: Add a cleaner suitable for use in heating and cooling systems, checking with heating appliance manufacturer’s instructions, and allow it to circulate, so it loosens debris within the heating system. This provides an opportunity for identifying any system components that may require replacing/upgrading to futureproof for low temperature systems, such as radiators, balancing TRVs and hot water cylinders.
Step 2 System Flush: A range of methods are detailed further in this guidance
Step 3 Install an inline filter: A requirement since 2019, providing clarity on difference between an inline filter and a strainer.
Step 4 Protect: Add an inhibitor that has passed BS 9593 Testing requirements, following the appliance manufacturer and inhibitor guidance and allow it to circulate through the system. For low temperature systems the use of an antifreeze and biocide should be considered.
Step 5 Test: Use an onsite test kit that is suitable for the chosen inhibitor to test the inhibitor level.
Step 6 Maintain: Annually test inhibitor levels, recording on Benchmark Online; every five years either carry out a full laboratory test or re-dose with the inhibitor.
HPA Chief Executive Charlotte adds: “We are fully committed to supporting heating engineers throughout the transition to low-carbon heating and providing insights on standards and Building Regulations guidance.
“Ensuring high water quality is crucial for all hydronic heating systems, and various approaches to corrosion protection are possible to enhance longevity and performance. We are pleased to contribute to the new guide with particular considerations for heat pump installations, and we have updated our HPA Commissioning Checklists to further assist installers.”
The guidance also highlights the importance of Benchmark Online, which provides a digital record for installation and servicing, enabling engineers to track key data such as inhibitor concentration and water quality. This ensures systems remain compliant and efficient throughout their lifespan.
The paper can be downloaded from the HHIC website at hhic.org.uk
