A thermostatic mixing valve (TMV) is a specially designed plumbing valve that carefully mixes hot and cold water to control hot water outlet temperatures to safe levels. TMVs are used in health,social care and education environments to protect people by reducing the risk of scalding from very hot water from showers, baths and wash hand basins.

Children and the elderly are particularly at risk from scalding from hot water with accident statistics showing that nearly 600 people suffered serious scald injuries in the UK each year. 75% of the victims of severe scalds were children under five years of age. Additionally, the figures also show that older people are at particular risk with those over the age of 65 accounting for almost two thirds of all fatalities in the UK.

Regular in-service testing of TMVs is essential to ensure they operate correctly, delivering safe water temperatures between 39°C and 43°C. This is the recommended temperature range for hot water outlets where a TMV is installed.

All TMVs should be tested and the results compared to those recorded during the original commissioning stage. Where there is no significant change to the outlet temperature (≤ 2°C) and the failsafe shut-off activates as it should, the TMV is considered to be operating correctly. However, if the water temperature has increased by more than 2°C or the failsafe does not work, a full TMV service plus recommissioning, or valve replacement will be required.

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There are currently 2 schemes in operation for the accreditation and usage of TMV valves TMV2 & TMV3

  • TMV 2 Scheme
  • TMV 3 Scheme
  • TMV Servicing & Maintenance
  • TMV Selector Chart

The TMV2 Scheme is very similar to the TMV3 version but with one big difference: where the TMV3 scheme is intended to be used to certify valves for use in the high risk healthcare sector, TMV2 valves are specifically designed, built and tested for the domestic market.

From April 2010, England and Wales joined Scotland in requiring, as part of the building regulations, the control of hot water temperature to a safe maximum at the bath outlet in domestic bathrooms, which can be achieved by the fitting of a thermostatic mixing valve.

In Scotland, regulations came into force in 2006, requiring control of outlet hot water temperature for baths and bidets: this applies to all new build domestic properties where the building warrant was applied for after 1st May 2006 and is also a requirement in properties undergoing bathroom renovation works which involve the movement or replacement of the bath or bidet. In England and Wales, the revisions to Part G of the Building Regulations (Hot water supply and systems) effective from 1st

April 2010 include the requirement that baths in new homes are fitted with a protective device (ie a thermostatic mixing valve) to limit the temperature of hot water.

The TMV3 Scheme is the third party valve accreditation programme which is administered by Buildcert. It has been set up to test independently whether valves submitted are suitable for
use in high risk commercial healthcare applications within the UK. The performance testing required in order to comply is based on the NHS model engineering specification D08 for thermostatic mixing valves.

Other important factors are also considered: for instance, an applying company must also prove that they comply with ISO 9001 or a suitable equivalent quality control system, the valves are checked for correct marking so they can be identified inthe field, packaging and instructions are checked to makesure they conform to guidelines issued by Buildcert.

If Buildcert is satisfied that all the requirements of the scheme have been met, it will issue a certificate granting a five year period of approval for the TMV. The valve will also be entered onto the list of approved products which is kept on the Buildcert website and is updated regularly.

After five years, the manufacturer must resubmit the valve for another full TMV3 test procedure: if successful, a new certificate will be issued and the entire cycle starts over again.

This level of third party compliance testing is unheard of in the rest of the world and helps to keep the UK at the forefront of hot water safety and thermostatic mixing valve technology and product development.

TMV Servicing and Maintenance is carried out in 4 stages, each stage is recorded and logged which you keep in your H&S record folder (Ideally with your Legionella monitoring documents)

Visual Inspection

Examine each TMV to identify if the correct specification valve is fitted, good accessibility and if isolation valves are fitted.

Water Temperature

Measure and record the mixed water temperature to ensure it is between 39°C and 43°C.

TMV Failsafe Test

Perform an in-service TMV failsafe shut-off test, isolating the cold water supply.

Clean, Descale & Disinfect

Isolate each TMV and clean, descale and disinfect valve components and fine mesh strainers.

Managing the risks associated with scalding from hot water in schools, healthcare and social care settings is a simple but essential safety management process. Regular testing and TMV servicing will help to ensure scalding risks are managed effectively and should be seen as an essential component in and regulatory compliance and Legionella control programme.

tmv2 and tmv3 explained