14 May 2026

6 min read

TMV Valves Explained: What They Are & Why Landlords Need Them

Pipe Assassin Plumbing TMV fitting — chrome thermostatic mixing valve installed on copper pipework under a UK bathroom basin

A Thermostatic Mixing Valve (TMV) blends hot and cold water to deliver a safe, controlled temperature at the outlet — typically a bath, basin or shower. It is one of the most important pieces of plumbing hardware in any property where someone could be scalded.

What Does a TMV Actually Do?

UK hot water is stored at 60°C or above to kill Legionella. That temperature will scald a child or vulnerable adult in seconds. A TMV sits between the hot supply and the outlet, continuously sensing the blend temperature and adjusting the mix. If the cold supply fails, the TMV slams shut — this is the "scald-failure" feature.

TMV2 vs TMV3 — What's the Difference?

TMV2 — the domestic standard. Required on all new bath installations in UK dwellings under Part G of the Building Regulations.
TMV3 — the healthcare standard. NHS DO8 and HTM 04-01 specify TMV3 for hospitals, care homes, schools and any healthcare premises. Tighter tolerances and an even more aggressive scald-failure response.

Who Legally Needs a TMV in the UK?

Anyone fitting a new bath in a dwelling (Part G, 2010 onwards)
Care homes, sheltered housing, supported living — TMV3 throughout
Schools and nurseries — TMV3 on hand-wash basins and showers
HMOs in many local authorities — check your local landlord licensing scheme, because requirements vary
Any setting where the responsible person has identified scald risk in a written risk assessment

Why Annual Servicing Is Non-Negotiable

TMVs drift. Internal cartridges scale up, strainers clog, springs weaken. An out-of-spec TMV either fails closed (no hot water) or, much worse, fails open — delivering water hot enough to scald. The manufacturer requirement, mirrored in the published TMV servicing standard, is annual:

Inlet temperature check (hot and cold)
Outlet temperature check — should hold 38-43°C depending on outlet type
Cold-feed shutdown test (close cold inlet, outlet should stop within seconds)
Strainer clean
Recalibration to spec
Written record with date, valve location, results

Ninja Tip

In hard water areas across the South East — including most of Hertfordshire, Essex and north London — six-monthly servicing is sensible. Limescale will take a perfectly-fitted TMV out of spec inside a year if it isn't maintained.

What to Look for in a TMV Installer

WRAS-approved valves only — never builders'-merchant generics
Documented calibration with serial number, location and date
Annual recalibration contract available
G3 certification if working alongside unvented hot water cylinders

Pipe Assassin — 24/7 Emergency Plumbers

07956 645 527

Rapid 24/7 response. G3 certified. Insured to £5m.

Pipe Assassin fits and services TMVs across London, Herts and Essex from our Enfield base — see our Enfield, Hertfordshire and Essex water hygiene pages for fixed pricing.

Frequently Asked Questions

Are TMVs a legal requirement in UK rentals?

TMV2 valves are required on all new bath installations under Part G of the Building Regulations (2010 onwards). TMV3 valves are required in healthcare, schools and any setting where vulnerable users could be scalded. HMO licensing schemes often impose stricter local requirements.

How often should a TMV be serviced?

Manufacturer requirement is annual: flow-rate test, scald-failure (cold-feed shutdown) test, strainer clean and recalibration. In hard water areas, six-monthly is sensible. Skipping the service voids the compliance documentation that landlords and care providers depend on.

What does a TMV cost to fit?

Pipe Assassin fits TMV2 and TMV3 valves from £125 per valve including supply, fit, calibration to 38-43°C and certificate. Annual recalibration is £65 per valve. WRAS-approved parts throughout.

What temperature should a TMV be set to?

For baths, the recommended set point is 44°C maximum. Basins and showers are typically set to 41°C. Bidets and washbasins for the elderly or very young drop to 38°C. Pipe Assassin calibrates and verifies the temperature with a digital probe at first fit and at every annual service.

What's the difference between a TMV2 and a TMV3 valve?

TMV2 valves are tested to BS EN 1287 for domestic use — bathrooms, kitchens, general scald protection. TMV3 valves are tested to the NHS D08 spec for healthcare environments — they shut off faster on a cold-water failure and have tighter temperature tolerances. Care homes, hospitals and special-needs schools require TMV3.

Can a TMV fail dangerously?

Yes. An out-of-spec TMV can drift hot (a scald risk) or stick open during a cold-water failure (also a scald risk). Both failure modes are silent without a routine calibration test. That's why annual servicing is the manufacturer requirement, not just a recommendation.

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