New guide sets out G3 compliance for unvented hot water systems

A new technical guide has been published to help installers, specifiers and manufacturers navigate the regulatory requirements for unvented hot water systems as the transition to low-carbon heating accelerates. 

Guide content 

Unvented Hot Water Systems: Regulatory Compliance Explained addresses frequently asked questions on Approved Document G3 and the Water Supply (Water Fittings) Regulations for modern hot water installations. 

The guide is published by the Hot Water Association and HPA UK, and it has been developed in response to growing demand for clearer guidance for unvented cylinder installers, including those working with heat pump systems. 

It uses a practical question-and-answer format designed to support consistent interpretation of the regulations across the industry. 

Compliance points 

The guide says the regulatory framework for unvented hot water systems has not changed, regardless of whether the cylinder is heated by a gas boiler, heat pump, solar thermal system or another heat source – the same statutory safety requirements continue to apply. 

It sets out the legal requirements in Approved Document G3, including preventing stored water from exceeding 100°C and ensuring discharge from safety devices is conveyed safely. It also summarises Schedule 2 of the Water Supply (Water Fittings) Regulations, covering temperature controls, relief valves, expansion control and discharge arrangements. 

Installer responsibilities 

The publication says responsibility for compliance rests with the installer, designer or builder carrying out the work. 

It also highlights the importance of installer competence through recognised G3 qualifications or membership of a competent person scheme, alongside following manufacturer installation instructions. 

Stewart Clements, director of the Hot Water Association, said the guide is intended to explain how Approved Document G3 and the Water Regulations should be interpreted in today’s market. 

The guide is free to download at: https://tinyurl.com/24bjahex and https://tinyurl.com/mr2x9w79