TMV questions, answered

A thermostatic mixing valve blends hot and cold water to a set temperature before it reaches the tap, shower or bath. Inside is a temperature-sensitive element that adjusts the mix as conditions change, so the outlet temperature stays steady.

Because stored hot water needs to be at 60°C or more to control Legionella, and hot water in the pipes needs to stay at 50°C or above (55°C in healthcare). Turning it down would swap a scalding risk for a Legionella risk. A TMV lets you keep the system hot and the outlet safe.

Under basins, behind bath panels, in shower risers or built into the tap or shower itself. They should be as close to the outlet as practical, and somewhere you can get to them for servicing.

TMV2 is a certification scheme for valves in domestic-type settings, based on BS EN 1111 and BS EN 1287. TMV3 is for healthcare and care settings, with stricter performance requirements. There's more in our TMV2 vs TMV3 article.

At least once a year, and six-monthly is common in care and healthcare settings. New valves should be checked within the first few months. See how often should TMVs be serviced? for the detail.

We isolate the cold supply to the valve. A working TMV should shut off the flow, or reduce it to a trickle, within a few seconds. It proves that if the cold supply fails, nobody gets a blast of hot water.

Limescale, debris in the strainers, worn thermostatic elements and changes in supply temperatures or pressures are the usual causes. Regular servicing catches drift before it becomes a problem.

Most problems can be fixed with a clean, descale, recalibration or new cartridge. If parts aren't available, the valve keeps failing, or it's the wrong type for the setting, replacement makes more sense. We'll be straight with you about which.

Little-used outlets, including those with TMVs, should be flushed as set out in your Legionella control scheme. The water after a TMV is warm, so stagnation there is worth avoiding.

Typical maximums for vulnerable users are around 38°C for a bidet, 41°C for a shower, 41–43°C for a washbasin and 44°C for a bath. Your risk assessment may set different figures. Our compliance guide explains more.

There's no single law saying "fit TMVs", but you do have a duty to manage scalding risk. In care and healthcare settings, HSE expects hot water at outlets used by vulnerable people to be temperature-controlled.

It's the Department of Health and Social Care's guidance on water systems in healthcare premises. It includes guidance on specifying, commissioning and testing TMVs.

The whole of the UK. We specialise in London and the Home Counties, and cover the rest of the country too.

It depends on the number of valves, how easy they are to reach and what condition they're in. We quote a fixed price up front, usually per valve or per visit. Tell us about your site and we'll give you a figure.

A certificate with the readings for every valve, logbook entries, an updated asset register and a note of anything that needs further work.

Call us on 020 3633 6064 or use the quote form. We'll ask a few questions about the site, send a quote and agree a date that suits you.