A tap running in a domestic kitchen

What is a Thermostatic Mixing Valve, and how does it work?

A thermostatic mixing valve (or TMV) is simply a precision device used to mix hot and cold water together. They’re designed to reduce the risk of scalding, and in the UK they’re mandatory in all new buildings that have water immersion fittings such as baths.

These valves are usually installed directly onto the outlet itself, which means the mixing of hot and cold happens at the moment the water leaves the tap. There are regulations in place that determine how TMV valves should be installed and looked after, as if they’re not maintained correctly they can be responsible for bacterial contaminations such as Legionella being introduced into the water system.

TMV valves are used in many different water delivery systems.

How does it work?

At the point of installation, a pre-set water temperature is set. When the valve is then used, hot and cold water will enter it causing a thermal element inside to contract and expand. This contraction and expansion opens and closes the side valves, which control the supply of hot and cold water by mixing it together in the right quantities until the pre-set temperature is achieved.

Why do we need them?

These valves offer excellent protection against scalding by ensuring that water can only flow at safe temperatures. Research shows that more than 10 children aged four or under are burned by domestic hot water on a daily basis. Aside from young children, people who are also particularly at risk of injury or death from unregulated water temperature include the elderly, disabled, or those suffering a mental health episode. For this reason, TMVs are commonly used in healthcare facilities and care homes.

TMV valves help to prevent scalding from unregulated water temperatures.

What regulations are in place?

There are numerous laws that regulate the installation and use of thermostatic mixing valves in the UK, especially on business premises. You can view guidelines on the HSE website here. If these regulations are not adhered to, users become at far greater risk of bacterial contaminations such as Legionella. Legionella rapidly multiplies in water conditions that can be created by poorly installed or maintained TMV’s. Once the water system becomes contaminated, anyone who comes into contact with it will be at risk of contracting Legionnaires’ Disease. This can result in severe health complications, as well as heavy fines or even imprisonment for those who are subsequently held accountable for the outbreak.

Remember, we are always here to help. If you have any questions or require any further information on TMVs or water system management in general, just give our friendly experts a call on 0800 121 8808 today.

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