The use of Thermostatic Mixing Valves or TMVs is now recognised as an essential tool, helping to protect young children and vulnerable adults from serious injury caused by scalding hot water. While such plumbing valves can offer significant protection to their users, they can also create some serious water safety issues if they are not serviced and maintained correctly. In this guide our water safety specialists explain what a TMV is, where they are fitted and how they work. The guide then looks at UK Building Regulations, safety laws and guidance; and how the additional risks from waterborne pathogens such as Legionella bacteria can be managed through effective maintenance and servicing.

What is a thermostatic mixing valve or TMV?

A thermostatic mixing valve, or TMV, is a special valve used in plumbing systems which mixes hot and cold water together to control the water temperature to safe levels.

TMVs are an essential piece of equipment used to minimise the risk of scalding from very hot water and are now used in all sorts of situations.

Where are TMVs fitted?

UK Building Regulations demand that TMVs are fitted in all new buildings which have baths… they are commonly found fitted to taps and showers too.

In many schools, hospitals, and health and social care settings they are also essential to protect children, patients and other vulnerable people from the dangers of scalding hot water.

TMVs are usually installed close to the point where the shower or bath water comes out, so that it is mixed just before discharging from the tap or shower head.

The Building Regulations also detail exactly how thermostatic mixing valves should be installed.

Incorrect installation and poor maintenance of TMVs needs to be avoided as this can cause further problems including increased risks from bacterial contamination, including the dangerous Legionella bacteria which can cause Legionnaires’ disease.

Learn more about Legionnaires’ disease

How do thermostatic mixing valves work?

First, the installer of the shower, tap or other water outlet decides on the desired water temperature and pre-sets this on the valve… this would normally be between 39°C and 43°C.

TMVs are designed to deliver safe water temperatures between 39°C and 43°C

The hot and cold water then flows into the mixing valve when the tap or shower is switched on.

A special thermal element inside the TMV valve starts to expand and contract as the water temperature changes.

As the valve expands and contracts, this constantly adjusts the temperature of the water coming out of the tap, blending the hot and cold water to exactly the right temperature.

If for whatever reason the cold water supply fails the TMV will shut off the flow of water completely.

This fail-safe shut off feature eliminates the risk of scalding from a very hot shower or tap.

Ensure your TMVs are correctly maintained so they work to keep people safe

Why is hot water scalding protection so important?

The UK safety charity ROSPA highlight that thirteen children under the age of four are burned or scalded every single day in the UK.

Having TMVs fitted to taps, showers and baths helps to minimise this serious risk.

Installers using TMVs know that water only ever comes out of the valve at a safe temperature, which protects all customers and users against scalding injuries which in the worst cases can be fatal.

Very young children, the elderly and people who are unable to react quickly to a hazard are at particular risk from water supplies which are not fitted with a TMV.

For this reason, it is standard practice to have TMVs (TMV3) fitted to all water outlets in hospitals, healthcare facilities and care homes.

The Department of Health’s guidance document HTM 04-01 has a section dedicated to the use of TMVs in health and social care settings.

Learn more about HTM 04-01 and the use of TMVs

UK rules and regulations covering the use of TMVs

The UK has a range of laws, regulations and guidance which cover how TMVs should be installed and used on business premises.

The best place to start your search for relevant guidance is on the Health and Safety Executive website or speak to an expert such as Water Treatment Services.

Under the Health and Safety at Work etc. Act 1974, companies have a legal duty to make sure that they are following the HSE codes of practice and guidance properly to ensure people are safe from harm.

If they fail to follow the HSE’s advice, there is a greater risk of scalding together with other risks including the build-up of dangerous waterborne pathogens.

TMV maintenance and legionella control

A good example of the types of contamination of the water systems that can occur in poorly maintained TMVs is Legionella bacteria.

Legionella is the bacterium that causes Legionnaires’ disease and it can grow and multiply very quickly in water systems with TMVs which are not installed or maintained properly.

If the bacteria is present in the water system, people who are exposed to the contaminated water are at risk of developing the potentially fatal Legionnaires’ disease.

If there is an outbreak of disease because of negligence on behalf of the person responsible for managing that risk, this can result in civil prosecution and litigation.

Penalties can include heavy fines, or even imprisonment… so it’s best to understand the law and follow it to make sure people are kept safe from both scalding and legionella.

Expert water safety and legionella control solutions

Water Treatment Services offer a comprehensive range of water safety solutions including TMV servicing and maintenance, and the management of legionella risks to support businesses and those responsible for the safety of engineered water systems in the workplace.

Find out how our water safety experts can help you manage your water systems, maintain regulatory compliance and so keep people safe..

With offices in London serving the South and South East England, Manchester (North West), Birmingham (Midlands), Bristol (South East England and Wales), Leeds (North and North East) and Glasgow (Scotland), supported by regional teams of specially trained engineers, water specialists and technicians we offer cost effective legionella risk assessments, training, water testing and other risk management solutions to businesses throughout the UK and Internationally.

Contact us today to learn how our expert water safety and legionella control solutions can help you.