Horne Engineering have designed and developed the Heatstat T2 (TMV2) thermostatic mixing valve specifically for the domestic market. Additional information about this market is contained in our newsletters,


Thermostatic Mixing Valves and the Domestic Market: The Facts - ISSUE 2'.

'Thermostatic Mixing Valves and the Domestic Market: The Facts - ISSUE 1'.

TMV2 - Reducing the risks from hot water.
PHAM News, December 2003/January 2004.

By installing a thermostatic mixing valve, you can help to reduce the number of serious injuries caused by hot water which is simply too hot. Denise Jones reports on the launch of the TMV2 scheme, designed to prevent the risk of accidental scalding in domestic bathrooms.

Hot water is the number one cause of severe scalding injuries among young children, and every year anaverage of 437 children under five are seriously scalded in the bath. Taking only seconds to occur, it may lead to many years of painful treatment for the child, and leave many parents experiencing a lifetime of guilt. Now, with the introduction of the BuildCert TMV2 scheme, installers have a key role to play in promoting the use of TMV2 products and thereby helping to resolve the problem of bath water scalds in the home.

The Child Accident Prevention Trust (CAPT), with financial support from the Department of Trade and Industry through its Consumer Safety Modernisation Fund, has worked with different interest groups. It has succeeded in bringing together key players in health, housing, manufacturing and accident prevention, to achieve a technical solution to the problem of child scalding injuries. The Thermostatic Mixing Valve Manufacturers Association (TMVA) responded by encouraging manufacturers to develop a thermostatic mixing valve, the TMV2, specifically for use in domestic bathrooms. Although TMV3s have been in use for several years in hospitals, care homes and other similar establishments, these provide a higher specification than is needed in the home, and also require more maintenance than the new TMV2.

"As a direct result of this initiative to reduce bath water scalds among young children, manufacturers have risen to the challenge," says Dr Howard Porter, Director of the TMVA. "Now parents can have a TMV2 fitted by their plumber that will prevent a severe bath water scald occurring - or may even save a child's life."

Another important outcome of CAPT's work has been the opportunity to influence housing policy through review and consultation processes. This has resulted in the Housing Corporation including the installation of TMV2s in its housing standards recommendations relating to new-build and refurbished housing association properties. In the first year, between 6,000 and 10,000 families are set to benefit from this.

Clive Clowes, Assistant Director from the Housing Corporation remarks: "By including TMV2 installation in our housing standard recommendations we are sending a clear signal to housing associations that we are serious about seeking to protect the most vulmerable members of society from severe bath water scalds. The new TMV2 will also help to ensure that those in charge of properties comply with their duty of care responsibilities."

Although currently there is no legal requirement for builders to install TMV2, the cost to do so in new builds is negligible, and as Jonathan Rees, Director of Consumer and Competition Policy at the DTI, points out: "The simple message is, prevention makes sense. For a small initial outlay, the issue can be resolved."

So what is the TMV2 and how does it work?
The TMV2 is a new generation of thermostatic mixing valves designed to prevent scalding in domestic situations. The product will accurately maintain the pre-set temperature of the bath water, even if the water pressure varies, when other appliances are used. Hot and cold water entering the valve is mixed to a temperature pre-selected by the user or installer.

This is achieved automatically by a thermally sensitive mechanism within the valve that proportions the amount of hot and cold water entering the produce the required blend. The mechanism then automatically compensates for any variations on supply pressure or temperatures to maintain the pre-selected temperature. If the cold water supply fails for any reason, the thermostatic mixing mechanism will automatically shut down the flow to prevent the discharge of dangerously hot water.

Best practice says that the required water storage temperature for hot water is 60°C or above to prevent legionella, and with the hot outlet supplying water at above 50°C within one minute. These hot water delivery temperatures may be useful in some applications, but in bathrooms they are clearly too high. The temperature should ideally be between 37°C and a maximum of 46°C from the outlets, which allows for heat loss in metal baths. An effective way to achieve this is to use thermostatic mixing valves at, or very close to, the point of useto reduce outlet temperatures.

The TMV2 scheme ensures that valves for domestic properties meet the requirements of BS EN 1111 or BS EN 1287 as well as additional requirements. Dr Guy Franklin, Scheme Manager for BuildCert explains. "Valves conforming to these standards can maintain temperature stability at all times, and will limit the flow in case of cold water failure to protect the user from scalding."

Installation of TMVs
The installation, commissioning and testing of in-situ valves is very important, but should be within the capabilities of any competent plumber. However, unless these procedures are carried out to the manufacturer's instructions, and to all relevant standards, the protection given by TMVs cannot be guaranteed.

Before installation it is important to ensure that its specification is appropriate, for example, flowrates, pressures and water temperatures must be within the stated limits. Most valves can be installed in any orientation, provided the hot and cold supplies are connected to the appropriate inlets, and since the valves contain temperature sensitive components, soldering near the main valve body must be avoided.

Depending on the design, each TMV will have different space requirements. Because of required flowrates, a valve approved for low pressure may be significantly larger than the one approved for high pressure. This is particularly true for baths because of the high flowrates.

In bathrooms the products should ideally be positioned either inside a vanity unit, behind a bath panel or behind a pedestal, facilitate easy access for servicing. Each outlet should be fitted with its own TMV with pipework from the valve no longer thatn 2 metres. The length limit is part of the current guidance on the prevention and control of legionella. Additionally, the length of any spur to a TMV from a hot water recirculation system should not exceed 5 metres.

Commissioning and maintenance
When commissioning TMVs certain checks need to be made before adjusting the temperature setting. The designation of the TMV needs to match the application, the supply pressures and temperatures must be within the valve's operating range, and isolating valves and strainers must be provided.

The BuildCert TMV2 scheme recommends that the maximum hot water temperatures from the bath hot tap should be 46°C, having regard in particular for the margin of error inherent in TMV2s, and temperature loss in metal baths, especially in cold bathrooms. However, it is not a safe bathing temperature for children. The British Burns Association recommends 37 to 37.5°C as a comfortable level for children. With regard to showers and washbasins the ideal temperature should be 41°C, and for bidets 38°C.

Availability and cost
Since the market for TMV2s is new at this stage, the product will not be available through DIY retailers. This is because the manufacturers recommend that they are fitted by qualified plumbers and, for the moment at least, the valves will only be available through plumbers' and builders' merchants.

The price of the valves vary from around £50, rising to over £100 depending on a number of factors such as size, finish and specific design. For users, the cost will also vary depending on whether the valve is fitted as part of other plumbing work, or commissioned as a separate installation.

The TMVA's member companies all offer a comprehensive range of products approved under the BuildCert scheme. For a list of approved TMV2 valves, visit Buildcert's website: www.buildcert.com.

The impact of a child scald accident can be devastating and result in long term disability and disfigurement, and can be among one of the most distressing and painful injuries a child can receive. As well as the human costs, there is the financial burden upon health and social services - it can cost as much as £250,000 to treat one severe bath water scald.

Prevention of child scalding injuries is clearly a problem which can be dealt with in the longer term, but in the meantime, awareness needs to be raised amongst parents and carers to mimimise accidents. The Child Accident Prevention Trust is addressing the problem by raising the profile of accidental injury among decision-makers, practitioners and parents. So with better awareness from industry, commerce, parents and plumbers, together with advances in technology, hopefully this issue will eventually become a thing of the past.