TMVs sit where two duties meet. You have to protect people from scalding, and you have to control the risk from Legionella. Get the balance wrong one way and someone gets burned. Get it wrong the other way and you're growing bacteria in warm pipework. Here's how the rules fit together.
The legal starting point
The Health and Safety at Work etc. Act 1974 puts a general duty on employers and people in control of premises to keep others safe, and that includes residents, patients, pupils and guests. COSHH covers biological agents like Legionella. The HSE's Approved Code of Practice L8 and its technical guidance HSG274 (Parts 1 to 3, with Part 2 covering hot and cold water systems) explain how to control Legionella in practice.
HSG274 Part 2 is where scalding comes in. It recognises that stored hot water needs to be hot enough to control Legionella (60°C at the heater, and at least 50°C at outlets within a minute, or 55°C in healthcare premises) and that's too hot for vulnerable people. Where there's a scalding risk, it points to TMVs as the usual answer, and says they need regular checking and maintenance.
HTM 04-01
Health Technical Memorandum 04-01 is the Department of Health guidance on water systems in healthcare premises. It's written for the NHS, but plenty of care homes, clinics and housing providers use it as their benchmark because it's thorough. For TMVs it covers:
- Using TMV3-approved valves in healthcare settings
- Fitting valves close to the outlet to keep the warm mixed-water run short
- In-service tests after commissioning (at around 6 to 8 weeks and 12 to 15 weeks), then a routine interval based on how much the valve drifts
- Keeping records of every test and service
If you're an NHS trust or a private clinic, your estates team or Authorising Engineer (Water) will usually set the detail. We work to your written scheme.
BS EN 1111, BS EN 1287 and the TMV schemes
BS EN 1111 covers thermostatic mixing valves for high-pressure systems and BS EN 1287 covers low-pressure ones. The TMV2 scheme approves valves for domestic-type use against those standards. The TMV3 scheme approves valves against the higher-performance NHS specification for healthcare and similar settings. A valve's approval should match both the setting and the supply pressures it actually sees.
Recommended outlet temperatures
These are the maximum mixed water temperatures commonly used for TMV3 valves in healthcare guidance. Your site's written scheme may set its own figures, and domestic settings are often set similarly.
| Outlet | Typical maximum | Notes |
|---|---|---|
| Bidet | 38°C | |
| Shower | 41°C | |
| Washbasin | 41°C | Some healthcare hand-wash basins differ; follow your scheme |
| Bath | 44°C | Bath fill temperatures can be higher where a carer is present; follow your scheme |
For new homes, Building Regulations Part G requires hot water to baths to be limited to 48°C, which is why you'll find TMVs or similar devices on bath supplies in recent London flats.
How TMVs affect your Legionella risk assessment
Your Legionella risk assessment should list where TMVs are, and your written scheme should set how they're checked. A few things assessors and inspectors commonly pick up on:
- No list of TMVs, so nobody knows how many there are or where
- No service records, or records that stop a couple of years ago
- Long pipe runs of mixed water after the valve
- One valve serving lots of outlets, some of them rarely used
- Hot or cold supplies out of range, which a TMV can't fix
Our servicing visits and asset registers are designed to close exactly those gaps.
A note on the details. Guidance gets revised and your site may have its own requirements, especially in healthcare. Treat this page as a friendly overview, not a substitute for your risk assessment, written scheme or Responsible Person.
Common questions
Is TMV servicing a legal requirement?
There isn't a law that says "service your TMV every X months". But if you control premises, the law requires you to manage scalding and Legionella risks, and the HSE guidance says TMVs need regular maintenance. If something goes wrong, records of servicing are how you show you did what was reasonable.
Who sets the service interval?
Your written scheme of control, usually based on the risk assessment and the results of in-service tests. In healthcare, HTM 04-01 sets out the approach. We'll advise based on how the valves actually perform, including how badly London's hard water affects them.
Do housing providers need to follow HTM 04-01?
It's written for healthcare, so it isn't directly aimed at housing. Many housing associations and care providers adopt parts of it as good practice, particularly for supported and sheltered housing where residents are more vulnerable.
Got TMVs in London that need a look?
Tell us roughly what you've got and where. We'll give you a fixed quote and a date that works around your building.