Thermostatic mixing valves blend a hot and cold water feeds in order to ensure a safe and constant output temperature. Thermostatic mixing valves are rated as either TMV2 or TMV3 and may also be referred to as Thermostatic Blending valves too.
The TMV2 and TMV3 approvals are regulated by Buildcert and the TMV3 standard meets the NHS D08 specification. Due to the negligable difference in cost between TMV2 and TMV3 valves, TMV2 valves are rarely specified or sold. Especially since the TMV3 thermostatic mixing valves all exceed the TMV2 standard.
TMV3 thermostatic mixing valves are most commonly used in the healthcare and education sectors in order to protect the most vulnerable people from scalding from a high-temperature water supply. Generally TMV2 and TMV3 valves are sold for 15mm plumbing and in the case of high flow applications such as baths or showers 22mm. They are however usually for the purpose of reliability and safety (including minimising legionalla risk), specified one valve per outlet.