An installers’ guide to choosing TMVs

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Thermostatic mixing valves (TMVs) are vital for keeping people and water supplies safe. They are regulated by law and have been a legal requirement since 2010 in all commercial and domestic new builds.

It’s a sad fact that every year more than 500 people are admitted to UK hospitals after suffering from severe scald injuries at home. Some 90% of these are children. Scalding – and Legionnaires’ – are serious concerns associated with hot water systems.

As an installer, you can help to drastically reduce these shocking figures by simply selecting the correct TMVs for the job, protecting end-users and offering a safe built environment.

Our innovative TMVs are perfect for all installations, even in the smallest spaces, so here is our guide to choosing TMVs.

The right TMV for the job

Given the importance of helping fight off harmful Legionella bacteria while also delivering water at safe temperatures, it is vital that you select the right TMV for the job.

Each application must therefore be considered very carefully.

According to Part G of the Building Regulations and the TMV2 Scheme, TMV2 certified valves should be used in domestic, 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 also be tested annually to maintain the certification. In these settings, a single TMV can be used to serve multiple outlets, ideal for a group of basins in public toilets or showers in a gym.

However, in healthcare settings, a risk assessment should be carried out and TMV3 certified valves must be specified accordingly. Crucially, a valve must be installed to every water outlet identified in the risk assessment.

With a variety of TMVs to choose from, the first key point in this guide to choosing TMVs is to first understand the application. At RWC we offer a choice of TMVs from our Reliance Valves brand including Heatguard Dual and Ausimix, suitable for different types of application with the relevant TMV2 or TMV3 approvals.

Ausimix TMVs

Checking flow rates

The next point in our guide to choosing TMVs is regarding the selection of a TMV. It is essential it performs at the flow rate required for that specific application. For example, although TMV2 allows for ‘group mixing’ to multiple outlets – ideal for a group of basins, public toilets and showers in a gym – the valve must be sized accordingly to meet the demand.

If undersized, this could result in insufficient hot water reaching the outlets.

However, bear in mind that times are changing and more attention is being placed on using less water to help save the planet.

Many modern taps now have a built-in flow restriction. Even if that restriction is as low as 1lpm, instead of the typical industry standard of 4lpm, our Easifit TMV will still function as expected.

In order to make the right choice, installers should always refer to TMV product data sheets, which contain information and graphs on flow rates. If in doubt, consult the manufacturer.

easifit thermostatic mixing valve

Preparing to install the TMV

So, you’ve selected the right TMV for the job. What next in our guide to choosing TMVs?

Before installing the TMV, you must prepare and install the pipework. For group mix valves, make sure the TMV is placed as close to the first outlet as possible, to help prevent the risk of a stagnation point, which can lead to Legionella getting into the system.

For TMV3 installations, regulations stipulate that valves should be placed within two metres of the tap.

In healthcare and commercial installations, the valves have to be regularly maintained so we recommend placing them in a service hatch, or getting them surface mounted, rather than being hidden out of reach inside cavity walls.

Our Easifit TMV is perfect for this as it can be placed in the tightest of spaces with ease, allowing for painless and efficient maintenance.

Heatguard push fit

Correct installation is vital

It should go without saying, but it is essential that the TMV is installed correctly. If not, it will fail to regulate the temperature of the water effectively and could cause major disruption.

You can avoid issues by simply making sure the hot and cold feeds are plumbed the right way around and the correct adaptors are put on the correct valves.

There should also be service valves – either on the valve itself, or plumbed in on the pipework leading up to the TMV.

TMV testing, maintaining and servicing

The final point in our guide to choosing TMVs is that all TMVs need to be tested, maintained and serviced at intervals set by the relevant scheme. Each application has its own temperature requirement.

TMV2 valves should be checked by measuring the mixed water temperature, then isolating the cold-water supply to the TMV. When the valve shuts off, no more than 120ml can be allowed in the outlet in a minute to meet test requirements.

The same process is required for hot water – if the temperature has changed by 2°C or more, or the failsafe doesn’t work, a full service is required.

TMV3 valve installers must check the system is still operational six to eight weeks after installation, and at six-month intervals after that. If there’s a failure, installers must fix the issue and re-test the valve and return again in six weeks’ time.

Keep a checklist of every TMV that you are installing, the temperature that it has been set to and record that the failsafe function has been tested and is working correctly.

Copies of these records can be left with the building owner/landlord, helping to ensure that future testing and maintenance is done under the same temperature parameters.

At RWC we’re here to help you get the job done right and choose the best TMV for the application. To learn more about the different application, legislation and flow rate requirements of all our TMVs, get in touch with our technical team today.

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Richard Bateman

Product Marketing Manager Plumbing and Heating

About the author

A highly experienced and passionate professional, I have over 15 years' experience as a commercial and domestic plumber and hold NVQ Level 3 qualifications from City and Guilds

Since joining RWC in 2015, I began as a technical engineer, utilising my extensive knowledge to provide exceptional support. Currently, I am thrilled to be working with the marketing department as a Product Marketing Manager. 

This role allows me to combine my technical background with a keen eye for market trends, ensuring that RWC's products meet the evolving needs of the industry. With my wealth of experience and commitment to excellence, I am proud to serve as a spokesperson for RWC, sharing our innovative solutions and contributing to the growth of the plumbing and heating sector.