TMV2 vs TMV3: which valve do you actually need?

Look at the label on a thermostatic mixing valve, or in its paperwork, and you'll usually see "TMV2", "TMV3" or both. They sound like version numbers, as if TMV3 is simply the newer, better model. It isn't quite that. They're two separate certification schemes aimed at different kinds of building, and picking the wrong one can leave you with a valve that isn't suitable for the people using it.

January's a popular time for refurbishment planning and budget setting, so it's a good moment to get this straight before you specify anything.

What the schemes actually are

Both TMV2 and TMV3 are independent third-party certification schemes. A manufacturer submits a valve for testing, and if it meets the requirements for a particular use, it gets certified for that use. The certificate says which applications the valve is approved for (bath, shower, basin, bidet) and at what pressures.

So "TMV3" doesn't describe what's inside the valve. It tells you what it's been tested and approved to do.

TMV2: for domestic-type settings

TMV2 is the scheme for valves used in homes and similar settings. It's based on two European product standards:

• BS EN 1111, for thermostatic mixing valves on high pressure systems (such as combi boilers and unvented cylinders).
• BS EN 1287, for low pressure valves, typically on gravity-fed systems with a cold water tank in the loft.

On top of those standards, the TMV2 scheme adds some UK-specific requirements. You'll find TMV2 valves in houses and flats, general needs housing and plenty of commercial washrooms. They're also commonly used to meet the Building Regulations requirement that limits bath water to a maximum of 48°C in new homes.

TMV3: for healthcare and care settings

TMV3 is the scheme for valves used where the people using the water are more vulnerable. It's based on the NHS performance specification for thermostatic mixing valves in healthcare premises, which is tougher than the domestic standards in several ways, including how tightly the valve has to hold its temperature and how it behaves when a supply fails.

HTM 04-01, the Department of Health and Social Care's guidance on water safety in healthcare, expects TMV3 valves in healthcare premises. Care homes, nursing homes and many supported housing schemes use them too, as do some schools and nurseries where young children use the outlets.

The quick comparison

Dual-certified valves

Lots of valves are certified under both schemes. That's handy on mixed sites, such as a care provider with some general staff areas, or a housing association with both general needs and sheltered schemes. Using one valve type across the board makes spares and servicing simpler.

One thing to watch: a dual-certified valve may be approved for different applications or pressures under each scheme. Always check the certificate covers how you're actually using it.

So which one do you need?

Start with the people, not the plumbing. Ask who's going to be using that outlet.

• Could they be slow to notice or react to hot water? Older people, people with dementia, reduced feeling or limited mobility, patients and young children all fall into this group. Go for TMV3.
• Is it a healthcare building? Then HTM 04-01 points to TMV3.
• Is it a home or an ordinary workplace? TMV2 is usually fine, unless your risk assessment says otherwise.

Then look at the system. Is it high or low pressure? Are the hot and cold supplies balanced? A valve certified for the right users but the wrong pressures won't perform as it should.

A common situation

A typical scenario we see: a building changes use but the valves don't. Say a block of general needs flats is converted into supported housing for older tenants. The TMV2 valves under the basins and on the baths were perfectly reasonable for the original use. Now the people living there are more at risk, and the valves should be reviewed.

That doesn't automatically mean ripping everything out. Some valves might already be dual-certified. Others might be due for replacement anyway because of age or scale. Going outlet by outlet usually gives a sensible, affordable plan.

Whichever you fit, keep it serviced

A TMV3 valve isn't "safer" if nobody tests it. Both types drift, scale up and wear over time. Both need commissioning when they're fitted, early in-service checks, and regular servicing and testing after that. If you're wondering how often, we've covered it in how often should TMVs be serviced?

If you're planning new valves or replacing old ones, our installation page explains how we choose and fit them. For the wider rules on temperatures and testing, see the TMV compliance guide.