Thermostatic Mixing Valves (TMVs) play a critical role in controlling water temperature and reducing the risk of scalding in both domestic and commercial buildings. In higher-risk environments such as healthcare, care homes and education settings, correct valve selection, installation and ongoing maintenance is not just best practice – it is a legal and moral responsibility.

This article explains:

• What TMVs are and how they work
• The difference between TMV2 and TMV3 scheme valves
• Where each type should be used
• Servicing and testing requirements under HSG274 and HTM 04-01
• Common compliance pitfalls we see on site

What Is a Thermostatic Mixing Valve?

A Thermostatic Mixing Valve blends hot and cold water to a pre-set temperature and automatically maintains that temperature, even when system pressures or supply temperatures fluctuate .

If either the hot or cold supply fails, the valve is designed to shut down safely:

• Cold water failure → shuts off to prevent scalding
• Hot water failure → shuts off to prevent thermal shock

When installed and maintained correctly, TMVs significantly reduce the risk of serious injury from hot water outlets.

How TMVs Work (In Simple Terms)

Hot and cold water enter the valve and are mixed internally by a temperature-sensitive element (thermostat or thermistor). This element continually adjusts the mix to maintain the selected outlet temperature, compensating for pressure and temperature changes elsewhere on the system .

TMVs can be:

• Fixed temperature (locked by the installer or facilities team)
• Adjustable temperature
• Adjustable temperature and flow

In commercial and healthcare settings, outlet temperatures are normally locked to prevent user interference.

TMV Schemes Explained: TMV2 vs TMV3

All TMVs should be independently certified under the BuildCert scheme, but not all TMVs are suitable for all environments.

TMV2 – Domestic and Low-Risk Applications

TMV2 valves are designed primarily for domestic and standard commercial settings. They comply with BS EN 1111 / BS EN 1287 plus additional BuildCert requirements.

Typical TMV2 environments include:

• Private dwellings
• Hotels
• Standard housing association properties
• Schools (non-special needs)

TMV2 valves provide good temperature stability but are not suitable for high-dependency users who may not be able to react quickly to sudden temperature changes.

TMV3 – Healthcare and High-Risk Environments

TMV3 valves meet the stricter requirements of D08 / HTM 04-01 (and BS 7942) and are specifically designed for use where users are vulnerable .

TMV3 valves are required in:

• Hospitals and NHS facilities
• Care homes and nursing homes
• Mental health units
• Special needs schools
• Any setting with dependent or vulnerable users

These valves undergo more rigorous performance testing and are subject to stricter installation, commissioning and servicing regimes.

Where Should TMV2 and TMV3 Valves Be Used?

Guidance and legislation clearly define where each valve type should be installed. As a rule:

• TMV2 → general domestic and commercial use
• TMV3 → healthcare and care environments

Examples include:

• Hospitals – TMV3 at all baths, showers, basins and bidets
• Care homes – TMV3 throughout
• Private dwellings – TMV2
• Schools – TMV2 (TMV3 where occupants are severely disabled)

Always consult the relevant guidance and the Responsible Person when in doubt, as misuse of TMV types is a common compliance failure .

TMV Servicing and Testing – What the Guidance Requires

HSG274 (Part 2 – Hot and Cold Water Systems)

HSG274 requires TMVs to be:

• Included in the water risk assessment
• Inspected, tested and maintained by competent persons
• Serviced in line with manufacturer’s instructions

Failing or poorly maintained TMVs are a known contributor to both scalding risk and Legionella control failures.

HTM 04-01 (Healthcare Premises)

HTM 04-01 places additional emphasis on TMV performance in healthcare settings, including:

• Regular in-service temperature testing
• Fail-safe testing
• Scheduled internal servicing
• Accurate asset registers and records

TMV3 valves must be maintained to ensure:

• Stable outlet temperatures
• Correct reaction times to supply failure
• Clean internal components (to reduce biofilm risk)

Typical TMV Maintenance Intervals (Best Practice)

While exact frequencies depend on risk assessment and manufacturer guidance, typical expectations are:

• Temperature checks – 3 to 6 monthly
• Fail-safe tests – annually
• Full service (strip, clean, descale) – annually or as specified
• Replacement – where performance cannot be restored

Importantly, TMVs should never be adjusted to compensate for underlying system faults such as incorrect hot water storage temperatures.

Common TMV Compliance Issues We See

At GMS, we regularly identify:

• TMV2 valves installed in TMV3 environments
• Missing servicing records
• Valves that have never been commissioned
• Incorrect outlet temperatures masked by valve adjustment
• Inaccessible TMVs preventing safe maintenance

Any of these can result in enforcement action, increased risk to users, or both.

How GMS Can Help

GMS Services provides:

• TMV surveys and asset verification
• TMV servicing & maintenance
• TMV replacements
• TMV2 and TMV3 servicing and replacement
• Compliance reporting aligned with HSG274 and HTM 04-01
• Integration with Legionella risk assessments and written schemes

If you’re unsure whether your TMVs are compliant, or whether they are even the correct type, we can help you put it right.

Need advice or support with TMV compliance?
Get in touch with GMS Services today – we’ll help you stay safe, compliant and confident.