Thermostatic mixing valves are essential components of any hot water system. They are designed to blend hot and cold water to a safe and stable temperature, preventing scalding while allowing hot water systems to run at high enough temperatures to help prevent Legionella bacteria from breeding.
TMVs have been a required element of commercial newbuilds since 2010, and of buildings undergoing a ‘change of use’ since 2012. Additionally, the valves are regulated by the Thermostatic Mixing Valve Manufacturers’ Recommended Code of Practice for Safe Water Temperatures, the NHS Estates guidance note for safe hot water, and the Health and Safety Executive (HSE).
So, what do installers and contractors need to bear in mind when installing TMVs?
Do select the right TMV
Different TMVs should be used for different purposes, and in different situations. With a variety of TMVs to choose from, it is key to understand the application and the requirements of the environment first.
As suggested in Part G of the Building Regulations, which covers sanitation, water safety, and efficiency, and the TMV2 scheme, TMV2-certified valves should be used in commercial and public buildings. Under this scheme, TMVs must maintain a safe and stable temperature of under 48°C at all times, and quickly shut off in the event of hot or cold water failure.
In commercial applications, TMV2-certified valves must be tested annually to remain up to certification. In these settings, a TMV can be used for multiple outlets, which is ideal for a group of basins in a public toilet or showers in a gym.
On the other hand, there are situations where a TMV must be fitted to every water outlet identified. For example, in healthcare environments, where a risk assessment should be carried out, and TMV3-certified valves should be fitted to every outlet.
Don’t skimp on preparation
Preparation for fitting a TMV is equally as important as the process of installation itself. Before installing a valve, care should be taken in selecting the best location for the TMV.
For example, a group mixing valve should have a TMV located as close to the first outlet as possible, to prevent the possible creation of a stagnation point, which can lead to a build-up of Legionella bacteria.
The furthest outlet from the TMV cannot be more than 2°C cooler than the set temperature. For example, if the set temperature is 46°C, then the temperature at the furthest outlet cannot be less than 44°C for the installation to remain compliant with TMV2.
For TMV3 installations, regulations dictate that the valve must be within two metres of the tap it is connected to. Although best practice is to fit the valve as close to the tap or outlet as possible anyway, as this limits the number of potential Legionella risk points.
Due to the regular maintenance required for commercial and healthcare applications, the valve must undergo regular maintenance, and it is therefore advisable that the TMV is installed in an easily accessible location. This could be a maintenance hatch or a surface mount, for example.
For tighter spaces, Reliance Valves’ Compact Ausimix Telescopic TMV can be a solution. With adjustable union connectors, its application is flexible, especially in retrofit installations. It is also WRAS-approved and certified to both TMV2 and TMV3 standards.
Do check the flow rates first
Because the requirements for TMV applications are never the same, it is critical to choose a TMV that can perform at the needed flow rate. TMV2s, for example, allow for group mixing to many outlets, but the valve must be scaled to suit the demands. If the valve is too small, it may result in insufficient amounts of hot water reaching the outlets.
Installers should refer to a TMV’s product data sheet, which contains flow rate statistics and graphics. If they has any doubts, they should contact the TMV’s manufacturer for help.
Don’t allow for scalding
One of the major benefits of TMVs is that they prevent scalding. Installers who use TMVs know that water only ever comes out of the valve at a safe temperature, which protects users against scalding injuries, which in the worst cases can be fatal.
However, TMVs can only prevent scalding injuries if they are fitted and maintained correctly.
As a result, TMVs of the TMV3 standard are required to be installed on all water outlets in hospitals, healthcare facilities, and nursing homes.
The guidance document (HTM 04-01) Safe water in healthcare premises, from the Department of Health, includes a section on the use of TMVs in health and social care settings.
Extra points to bear in mind
If incorrectly installed, TMVs cannot effectively regulate water temperatures. This, in turn, means that the TMV will require ongoing maintenance and servicing, and, in healthcare applications, the outlet will be put out of use – potentially causing severe disruption.
It is therefore important that the hot and cold feeds are plumbed in the right way around, and that the correct adaptors are on the correct ports. Installers need to ascertain that there are service valves on the valve or on the piping going up to the TMV.
These steps are vital to ensuring that the TMV operates efficiently and that the water supply can be isolated for testing and maintenance purposes.
In addition, the difference in temperature between the hot water supply and the set mixed outlet temperature must not exceed 10°C to ensure the valve mixes correctly.
For example, if you wanted to achieve 46°C at the tap, then the temperature at the hot supply to the valve must be a maximum of 56°C. This differential reduces the risk of potential temperature spikes or drops out.
Installing TMVs is an essential skill in every plumbers’ arsenal, and, while the process can present a few speedbumps, it should not be a cause for headaches. As an integral part of any hot water system, it is important that TMVs are installed correctly, but by keeping these do’s and don’ts in mind, best practice will prevail.
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