Historically a T&PR valve has been used to ensure that the hot water temperature of an unvented cylinder never exceeds 100°C. However, Part G3 of the Building Regulations and the UK Water Regulations has recently been revised to allow alternative approaches to be taken, as long as they offer an equivalent degree of safety.
With large market share, unvented cylinders are now a popular choice for new build and refurbishment projects and, as a result of stringent safety requirements, which have been in place since their introduction to the UK market in the 1980s, they enjoy an excellent safety record.
The correct installation practises for unvented cylinders installed in the UK are set out in Part G3 of the Building Regulations and the UK Water Regulations.
Part G3 of the Building Regulations calls for two independent levels of safety control and a limitation of 100°C, and, until recently, stated that a T&PR valve must be used for this purpose. In 2010 Part G3 was amended to allow alternative approaches to be used, as long as they offer an equivalent degree of safety to a T&PR valve. The requirement for two levels of safety control, and for the system to not exceed 100°C, remains. In August 2011 the UK Water Regulations were amended to bring their requirements into line with those of Part G3.
However, although other solutions are now acceptable, the emphasis is still very much on the use of T&PR valves. To paraphrase, clause 3.18 of Part G3 suggests that ‘an acceptable approach to providing these two levels of safety would be to provide a non self resetting energy cut-out and a T&PR. Alternative approaches are acceptable provided they provide an equivalent degree of safety’.
When talking about this issue, the term ‘relaxation’ is used on the WRAS (Water Regulations Advisory Scheme) website, but we think it would be better to refer to the changes as an amendment – as the essential safety requirements remain unchanged.
It is also difficult to see what alternative approaches could be used. Being a totally independent, self-contained mechanical device, which doesn’t rely on wiring, a T&PR valve is by far the most effective, safest, reliable and straightforward method to keep hot water temperatures from exceeding 100°C. Furthermore, installers have been fitting T&PR valves and their associated discharge pipework since unvented water heaters were allowed in the UK Water Regulations in 1985.
Some installers might be led to believe that if a cylinder is installed as part of a heating system package then the boiler’s over-temperature control would provide the second level of safety (hence complying with clause 3.18 of Part G3). This may be the case where the cylinder is fully integrated with the boiler, however, in the UK 90% of cylinders are bought independently to the boiler – so there might not be a suitable degree of control.
In addition, if an indirect cylinder is fitted with a back-up immersion heater (as is often the case) then an alternative secondary level of control will still be necessary, as the immersion heater could well become the primary source of heating should the boiler fail, and would then be operating independently.
The Department for Communities and Local Government (DCLG), which is responsible for Part G3 of the Building Regulations, has recently commissioned an independent review of the safety devices used on unvented systems, and is analysing whether alternative approaches to T&PR valves offer the same degree of safety protection.
The majority of UK manufacturers aren’t in favour of removing the requirement for fitting T&PR valves, especially on stand-alone cylinders that operate independently to a boiler.
Furthermore, although they aren’t required in most European countries, T&PR valves are still the preferred choice for unvented systems in the US, Australia, New Zealand and South Africa.
Until the DCLG report findings are published we would strongly urge the industry to continue using unvented cylinders with T&PR valves.
Installers should also be advised to never remove a T&PR valve from an existing installation, as this could seriously compromise safety.