What is a TMV Valve?

Joe Pettigrew
6 days ago
3 min read

Thermostatic Mixing Valves, commonly known as TMVs, are critical safety components in plumbing and water systems. Designed to blend hot and cold water to a safe, controlled temperature, TMVs are widely used in commercial, healthcare, educational, and residential settings. Their primary purpose is to prevent scalding injuries while ensuring that water systems remain legionella-compliant.

In this article, we’ll explain what TMV valves do, how they work, where they’re required, and how to maintain them properly- - all in plain terms tailored for facilities managers and property professionals.

What Does a TMV Valve Do?

How TMVs Work

A TMV valve automatically mixes hot and cold water to deliver water at a consistent and safe outlet temperature. Inside the valve, a thermostatic element expands or contracts based on temperature fluctuations. If cold water supply fails, the valve shuts off or significantly reduces hot water flow, protecting users from scalding.

This makes TMVs especially valuable in environments where vulnerable individuals - such as children, the elderly or those with reduced mobility - might be exposed to high-temperature water.

Legal and Regulatory Importance

In the UK, TMV2 and TMV3 regulations define performance standards depending on the type of premises:

TMV2: For domestic and general healthcare use (e.g., homes, schools, care homes).
TMV3: For high-risk environments such as hospitals and NHS buildings.

Installation of TMVs in certain types of properties is a legal requirement under the Building Regulations (Part G), especially where risk of scalding is deemed significant. They also help support compliance with HSG274 Part 2 by maintaining controlled water temperatures to reduce legionella bacteria growth.

Where Should TMV Valves Be Installed?

Common Locations

TMVs are typically fitted close to outlets, including:

Wash hand basins
Showers
Baths
Healthcare sinks
School facilities
Disabled toilets and changing areas

Installing TMVs as close as possible to the point of use ensures the greatest level of control and safety.

Sector-Specific Applications

Facilities managers overseeing hospitals, schools, hotels, and public buildings will often be responsible for hundreds of outlets where TMVs are mandatory. Ensuring each valve functions correctly is not just a best practice - it’s a duty of care.

Why Regular TMV Maintenance Is Critical

TMV Servicing and Testing

Over time, TMV valves can suffer from scale build-up, component wear, or bacterial contamination. This is why regular servicing is essential, and why many facility managers implement routine TMV testing and calibration as part of their planned maintenance schedules.

Standard practice usually involves:

Annual performance testing to check temperature stability
Strainer and check valve cleaning
Disinfection and descaling
Temperature adjustment, if needed
Verification that the valve shuts off correctly in failure scenarios

For guidance on how often to test and service TMVs, check out our Planned Preventative Maintenance page.

Risks of Neglect

A poorly maintained TMV can become stuck, fail to shut off in the event of water supply issues, or deliver unsafe water temperatures. This increases risks of:

Scalding injuries
Non-compliance with regulations
Waterborne disease outbreaks, such as Legionnaires’ disease

Proper record-keeping and asset tracking of your TMVs is just as important as the maintenance itself.

Choosing the Right TMV for Your Facility

Factors to Consider

When selecting TMVs for your building, consider the following:

Type of use: Public vs. private, high-risk vs. low-risk environments
Approvals required: TMV2 or TMV3
Pipe size and flow rate
Access for servicing and inspection
Water pressure and temperature variations

Using the wrong type of TMV, or installing it incorrectly, can lead to costly compliance failures and unsafe conditions. Our Mechanical Services overview gives more detail on our installation approach.

Summary

Thermostatic Mixing Valves are a cornerstone of safe water delivery systems in both public and private buildings. Understanding what they are, how they function, and why they must be maintained will help facilities managers stay compliant, protect users, and avoid liability.

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