The Hot Water Association (HWA) and HPA UK has published a new technical guide to help installers, specifiers and manufacturers navigate the regulatory requirements for unvented hot water systems as the transition to low-carbon heating accelerates.
The publication, ‘Unvented Hot Water Systems: Regulatory Compliance Explained’, addresses some of the most frequently asked questions surrounding the regulations and requirements of Approved Document G3 and the Water Supply (Water Fittings) Regulations to modern hot water installations. It has been developed in response to growing need for clearer guidance for all unvented cylinder installers, including those in heat pump systems as they become increasingly common for domestic heating.
New technologies but statutory safety requirements remain
Although heating technologies are evolving rapidly, the guide makes it clear that the regulatory framework governing unvented hot water systems has not changed. Regardless of whether an unvented cylinder is heated by a gas boiler, heat pump, solar thermal system or another heat source, the same statutory safety requirements continue to apply.
Stewart Clements, Director of the Hot Water Association, said: “The growth of heat pumps has raised understandable questions about how existing regulations apply to new system designs. This guide has been developed to explain to installers and specifiers how Approved Document G3 and the Water Regulations should be interpreted in today’s market.
“Innovation is essential if the industry is to meet its net zero ambitions, but safety must remain paramount. Our aim is to support the industry with practical guidance that promotes consistent compliance while allowing manufacturers to continue developing new solutions.”
Nancy Jonsson, Technical Consultant to the HPA UK commented: “This Frequently Asked Questions has been developed as the result of collaborative efforts from leading industry experts. It provides installers with useful reminders when fitting unvented hot water cylinders and highlights the importance of following existing regulations and cylinder manufacturer’s instructions to ensure that safety devices are correctly fitted. The Heat Pump Association UK is committed to providing clear, practical information to the sector and support installers as the demand for low-carbon heat pump continues to grow.”
The guide explains the legal requirements contained within Approved Document G3, including the need to prevent stored water exceeding 100°C and to ensure that any discharge from safety devices is conveyed safely. It also summarises the key provisions of Schedule 2 of the Water Supply (Water Fittings) Regulations, covering temperature controls, relief valves, expansion control and discharge arrangements.
Recognising that some manufacturers deploy alternative third party approved control strategies within integrated boiler or heat pump cylinder packages, the guide explains when these approaches may be acceptable. Installers are reminded that if they wish to use a different approach, any deviation from a third party approved product configuration should first be supported in writing by the manufacturer and agreed with the relevant Building Control Body.
The publication also reinforces that responsibility for regulatory compliance rests with the installer, designer or builder undertaking the work. It highlights the importance of installer competence through recognised G3 qualifications or membership of a competent person scheme, alongside following manufacturers’ installation instructions.
Produced jointly by HWA and HPA UK, the guide adopts a practical question-and-answer format to address the issues most frequently encountered by installers working with unvented hot water systems. It is intended to encourage consistent interpretation of the regulations across the industry while supporting the safe deployment of low-carbon heating technologies.
The guide, ‘Unvented Hot Water Systems: Regulatory Compliance Explained’, is available to download free of charge from the Hot Water Association website and HPA UK website.
Source: https://www.hvnplus.co.uk/news/new-industry-guide-provides-clarity-on-g3-compliance-for-unvented-hot-water-systems-27-07-2026/
