Selecting, commissioning and maintaining TMVs; the bath ceiling and lower limits for vulnerable users.
Storing hot and controlling delivery
A thermostatic mixing valve (TMV) blends hot and cold water to regulate the outlet temperature while the hot-water system maintains its hygiene controls. Choose a valve suitable for the users, outlet and available supply conditions.
Its safety response depends on correct installation and operation within its specified limits. Check inlet temperatures and pressures, minimum flow, clean strainers and the required difference between the hot inlet and mixed outlet temperatures. Measure the blended temperature and test the cold-supply-failure response using the valve’s commissioning procedure. A fitted valve still needs every one of these checks.
The bath limit and vulnerable users
For a new dwelling in England, the fixed-bath hot-water supply is limited to a maximum of 48 °C. That ceiling does not make 48 °C a suitable bathing temperature for everyone. Where vulnerable people are at risk during whole-body immersion, water must not exceed 44 °C; some users need a lower temperature or assistance. A suitable Type 3 TMV is required where the significant scalding risk calls for that protection.
Maintaining the protection
- Preserve the required storage and distribution hygiene regime.
- Fit the valve close to the outlet and minimise stagnant blended-water pipework.
- Verify the outlet temperature under the actual supply conditions and secure the setting as specified.
- Maintain and test the valve at the required intervals, recording results and correcting failed checks.
Check the hot inlet for distribution-temperature monitoring and the blended outlet for scald protection. They have different targets.
Valve types and checks
- TMV2 covers general domestic applications, while Type 3 approval addresses the more demanding healthcare performance specification. Select the designation for the outlet and assessed users. Approval does not set the temperature for you: commission and secure the setting, then verify the safety response within the model’s limits.
- A marked setting is not the actual outlet temperature. After adjustment, measure the delivery under the required conditions and record it as a comparison for later checks. During the failure test, use the model’s stated temperature and residual-flow criteria; some valves permit limited cool residual water.
- Legionella can grow in warm water, roughly 20–45 °C. Adequate heating inhibits growth and kills bacteria progressively, with effectiveness depending on achieved temperature and exposure time. A hot thermostat setting does not mean every part of the system has been treated. Keep the specified hygiene regime and manage scald risk separately at the outlets. At 60 °C, an adult can suffer a serious scald in roughly five seconds; young children may be injured sooner. Injury time varies with the person and exposure, so this is not a safe contact allowance.
- A point-of-use water heater storing no more than 15 litres is checked to confirm it operates at 50–60 °C (55 °C in healthcare premises), or that the installation has a high turnover.