What is the difference between TMV2 and TMV3?
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Key points
- TMV stands for thermostatic mixing valve: it blends hot and cold water to a safe outlet temperature so the system can run hot enough to control legionella without scalding the user.
- TMV2 and TMV3 are the same valve certified to two schemes: TMV2 for general and domestic use (BuildCert, BS EN 1111 / BS EN 1287), TMV3 for healthcare (NHS D08 specification).
- TMV3 is the stricter standard: tighter tolerances and a stricter in-service checking regime, used where occupants are more vulnerable, in settings covered by HTM 04-01.
- A TMV3 valve can be used in a TMV2 setting, but a TMV2 valve is not approved where TMV3 is required.
- Whichever scheme applies, the valve is deliberately kept warm, so it must be serviced on a schedule as part of legionella control.
TMV2 and TMV3 are the same kind of valve, a thermostatic mixing valve, certified to two different approval schemes for two different settings. TMV2 covers general and domestic premises; TMV3 covers healthcare, under the NHS D08 specification, with tighter tolerances and stricter checks. The valve's job is the same in both cases: blend hot and cold water down to a safe temperature at the outlet so nobody is scalded.
If you have found this page trying to work out which valve you need, or simply what the letters mean, this covers what a TMV is, how the two schemes differ, which one applies to your building, and why the valve matters for legionella as well as scalding.
What a TMV is, and what TMV stands for
TMV stands for thermostatic mixing valve. Hot water is stored hot, at 60°C, so that the temperature kills legionella (see temperature control). Water that hot would cause a serious scald in seconds, so it cannot be delivered straight to a basin or shower. A TMV solves that by blending the stored hot water with cold, close to the outlet, to deliver water at a safe, stable temperature, usually around 41°C at a basin or shower and up to about 44°C at a bath.
An approved TMV also has a fail-safe. If the cold supply fails, the valve shuts the flow off rather than letting scalding hot water through. That combination, a stable safe temperature plus a fail-safe shut-off, is what makes it a safety device rather than a simple mixer tap.
TMV2 versus TMV3: the difference
The valve is mechanically similar in both cases. What differs is the approval scheme it is certified to, the tolerances it must meet, and the setting it is approved for.
| TMV2 | TMV3 | |
|---|---|---|
| Approval scheme | BuildCert TMV2 scheme | NHS D08 specification (BuildCert TMV3) |
| Standard | BS EN 1111 and BS EN 1287 | NHS D08, tighter tolerances |
| Intended setting | Homes, offices, schools, most commercial premises | Healthcare: hospitals, care homes and settings under HTM 04-01 |
| Occupant risk | General | Higher: patients and residents more vulnerable to scalding and infection |
| In-service checks | Serviced at the interval the risk assessment sets, commonly annual | Stricter: commissioning checks at 6 to 8 and 12 to 15 weeks, then a set cycle |
Source: BuildCert TMV2 and TMV3 (NHS D08) schemes. A TMV3 valve may be used where TMV2 is acceptable; a TMV2 valve is not approved where TMV3 is required.
Which one you need
The setting decides it. For a home, an office, a school, a shop or most commercial buildings, a TMV2 valve is the approved choice. For a hospital, a care home, or any healthcare setting managed under HTM 04-01, where patients may be elderly, very young, sedated or otherwise less able to react to hot water, a TMV3 valve is expected. The dividing line is the vulnerability of the people using the outlet, not the type of tap.
Your legionella risk assessment should record which standard applies at each outlet and why, because a mixing valve is both a scald control and, being warm, a point that needs managing for legionella.
Free legionella risk assessment template
A structured Word document following the five-step approach in ACOP L8. Covers risk identification, written scheme, monitoring, and records. If it isn't written down, you can't evidence it.
Follows ACoP L8 and HSG274 Part 2. Free. No spam.
Why the valve matters for legionella, not just scalding
A TMV controls scalding, but in doing so it creates a small legionella risk that then has to be managed. The blended water it produces, at roughly 38°C to 46°C, sits squarely inside the legionella growth range of about 20°C to 45°C. The valve body, its strainers and any short length of blended pipework after it are therefore warm, and warm wetted surfaces grow biofilm and scale.
This is why a TMV is not fitted and forgotten. It is sited as close to the outlet as possible so there is very little warm water sitting downstream, and it is serviced on a schedule: inspected, cleaned, descaled, disinfected, and its fail-safe shut-off tested. TMV3 valves in healthcare carry the stricter checking regime precisely because the people they serve are the least able to tolerate a failure.
Where this fits in your legionella controls
Choosing and maintaining the right mixing valve is one line in a wider scheme. The hot water feeding the valve should still be genuinely hot, stored at 60°C and reaching the inlet at 50°C (55°C in healthcare) within a minute; the cold should stay below 20°C; and the valve should be serviced and recorded like any other control. All of this sits under the duties in ACOP L8 and the detail of HSG274, with the healthcare additions in HTM 04-01. Fitting a TMV does not make a system safe on its own; it is the maintained valve, the hot supply behind it and the record of both that manage the risk.
Free legionella risk assessment template
A structured Word document following the five-step approach in ACOP L8. Covers risk identification, written scheme, monitoring, and records. If it isn't written down, you can't evidence it.
Follows ACoP L8 and HSG274 Part 2. Free. No spam.
Frequently asked questions
What is the difference between TMV2 and TMV3?
They are the same type of valve certified to two different schemes for two different settings. TMV2 valves are approved for general and domestic use, certified to BS EN 1111 and BS EN 1287 under the BuildCert TMV2 scheme. TMV3 valves are approved for healthcare use under the NHS D08 specification; they meet tighter performance tolerances and carry a stricter in-service checking regime. A TMV3 valve will do a TMV2 job, but a TMV2 valve is not approved for a healthcare application that calls for TMV3.
What does TMV stand for?
TMV stands for thermostatic mixing valve. It is a valve that blends stored hot water with cold to deliver water at a safe, stable temperature at the tap or shower, protecting the user from scalding. The blending happens automatically: if the cold supply fails, an approved TMV shuts the flow off rather than delivering scalding hot water.
What is a TMV valve?
A TMV valve is a thermostatic mixing valve, a device fitted near a tap, basin, bath or shower that mixes hot and cold water down to a safe delivery temperature, typically around 41°C at a basin or shower and up to about 44°C at a bath. It lets the rest of the water system run hot enough to suppress legionella while still delivering water that will not scald the user. Because its blended output is warm, the valve itself needs servicing on a schedule.
Do I need a TMV2 or a TMV3 valve?
For a home, an office, a school or most commercial premises, a TMV2 valve is the approved choice. For healthcare premises, hospitals, care homes and other settings covered by HTM 04-01 where occupants are more vulnerable to scalding, a TMV3 valve certified under the NHS D08 scheme is expected. If you are unsure, the deciding factor is the setting and the vulnerability of the people using the outlet, and your risk assessment should record which standard applies and why.
What is the D08 scheme?
D08 is the NHS specification that TMV3 valves are certified against. It sets tighter performance and safety tolerances than the general TMV2 standard, reflecting the higher scald risk to patients in healthcare settings, and it is why TMV3 valves carry a stricter regime of in-service checks after they are commissioned. A valve marked TMV3 has been tested and approved to that healthcare specification.
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