Are Your Thermostatic Mixing Valves (TMV’s) Maintained as required to prevent Scalding and Compliant as Part of Your Legionella Risk Management?

There are good reasons to install TMV’s in care homes, children homes, nursing homes and in locations where vulnerable people need protection from hot water scalding.

Thermostatic Mixing Valves (TMV’s) are not a fix and forget solution for scald protection.

Main Issues

  • Once installed TMV’s must be properly service and tested on a regular basis because scale and debris resulting from the quality of the incoming water supply can quickly lead to TMV failure and therefore to the possibility of scalding potential to users.
  • TMV’s are strictly regulated in terms of type of valve, approval of valve, installation and commissioning and in regular maintenance.  The NHS has the D08 Model Engineering Specification guide that ensures that TMV’s are fit for purpose, installed and commissioned correctly and services regularly.
  • TMV’s, if not maintained, could risk hot water back flow into the cold main supply, if no non return valve is fitted.  Hot water back flow could lead to Legionella water quality issues or potential scald risk in certain instances.
  • TMV’s are also a potential risk source for Legionella proliferation.  The pipe between the valve and point of use should be as short as possible to minimise the risk of Legionella bacteria breeding in optimum temperature conditions provided by TMV outlet warm water.  (40 degrees is ideal for Legionella growth.)

Brief Summary of Main Guidelines

  1. Type of valve TMV Valve
  • TMV is required for care homes and NHS properties.
  1. Correct installation, commissioning and set up according to manufacturers recommendations and the use. These include:
  • Water pressure, water temperatures of hot and cold feed
  • Location of the valve from point of use (close as possible but not longer than 3 meters).
  • Set up a valve to deliver the right temperatures, and check cold failsafe works correctly.
  1. Regular maintenance.
  • Annual service of valve to check performance, temperature stability, failsafe and clean of filters and valve body as required.
  • Monthly temperature checks of system both from a Legionella risk management point of view and from a scalding control point of view.
  • For Legionella risk control, the hot temperature feed should be at least 50 degrees C (after one minute) to a maximum of 60 degrees C for safe use.  The cold feed to the valve should be at less than 20 (after one minute).
  • The point of use temperature should be measured to ensure it is within 2 degrees C of the controlled set temperature to minimise scalding risk.
  1. Training
  • Adequate training and supervision should be provided to ensure that staff who maintain the premises, or assist vulnerable people, understand the risks and precautions.

For detailed information please refer to, Health Technical Memorandum 04-01: Supplement Performance specification D 08: thermostatic mixing valves (healthcare premises)


UKHCA Guidance – Controlling Scalding Risks from Bathing and Showering