FREQUENTLY ASKED QUESTIONS – THERMOSTATIC MIXING VALVES

What is a Thermostatic Mixing Valve?
Thermostatic Mixing Valves (TMV’s) accurately control water temperatures for bathing, showering and hand-washing. They maintain pre-set temperatures and can be fitted under baths and basins, be part of shower fittings, or as a feature of exposed hot and cold water mixers.

How does a Thermostatic Mixing Valve work?
Hot and cold water entering the valve is mixed to a temperature pre-selected by the user or installer. A thermally sensitive mechanism within the valve automatically proportions the amount of hot and cold water entering to produce the required blend. The mechanism then automatically compensates for any reasonable variations in supply pressures or temperatures within the design range to maintain the pre-selected temperature. In the event of cold water supply failure, the thermostatic mixing mechanism will automatically shut down the flow to prevent discharge of dangerously hot water. The flow will also be shut down in the event of a hot water supply failure to prevent thermal shock.

Why are Thermostatic Mixing Valves so important?
Over three quarters of severe scalds are suffered by children under five years of age, and almost three quarters of the fatalities from scalding are people aged 65 and over. By limiting water temperature and stopping sudden increases in water temperature, TMVs help to prevent scalding, which can cause very serious and even fatal injuries. Hot bath water is responsible for the highest number of fatal and severe scald injuries, every year around 20 people die as a result of scalds caused by hot bath water and a further 570 suffer serious scald injuries.
Young children and older people are most at risk from bath water scalds because their skin is thinner and therefore less tolerant to higher water temperatures than that of other age groups. As a result, they sustain scalds more quickly, at lower water temperatures and often with a greater depth of burn.
People with a reduced ability to perceive risk or react to hazardous situations – for example those with mental or physical disabilities – are also at greater risk of injury. TMVs help to protect the population from scalding injuries.

Requirements for Servicing and Maintenance of Thermostatic Mixing Valves

Once a Thermostatic Mixing Valve has been installed, the servicing and maintenance of a TMV becomes the responsibility of the site and those placed in charge of managing it. For example, should a scalding occur due to a faulty TMV, which had not been serviced, the blame would most likely lie with the site and not with the manufacturer. Therefore the purpose of in-service testing is to regularly monitor and record the performance of the thermostatic mixing valve. It is also imperative to ensure the TMV remains clear from scale deposits as this can significantly impact upon the performance of the valve.