04 May 2021

How Often Should a TMV Be Serviced?

A thermostatic mixing valve (TMV)

A thermostatic mixing valve (TMV) is a valve that combines hot and cold water to produce a temperature-controlled flow of water prior to it reaching taps, showers and other hot water outlets. Put simply, the device ensures the water temperature is always at a safe and comfortable level which prevents people from scalding themselves. Hot and cold water passes through the valve on its way out, ensuring it is a safe temperature by the time it reaches the water outlet.


To prevent bacteria such as legionella from breeding, hot water needs to be kept at a temperature of 60 degrees Celsius and circulated at a minimum of 50. As water at this temperature will scald the skin, it is therefore necessary to cool it for safe use. Using a TMV will blend the hot water with cold water at the point of discharge, to produce a flow at a safe and comfortable temperature of around 38-41°C.


Fail-safe, thermal shutdown

Whilst temperature control can be achieved by any basic mechanical mixer tap/shower, the primary feature of a TMV is that it offers additional safety via a thermal shutdown mechanism. In simple terms a thermal shutdown or fail-safe stops the flow of water through the outlet regardless of whether or not the outlet remains in an ‘open’ position (i.e turned on) and does so in the event that water from the primary hot or cold supply fails to reach the outlet for blending.  This feature prevents scalding and or thermal shock of the user in such instances. Standard mechanical mixing cannot achieve this so in the event of cold water failure would continue to deliver scalding hot water if the outlet remained in the “open”.

This is of particular concern in circumstances of “whole body” submersion e.g baths or showers, however in situations where users are vulnerable, they should also be installed for sinks. 



What are the regulatory requirements in hospitals, health and social care settings?


Hospitals, social care, healthcare and similar properties that fall under the Care Standards Act 200 should be fitted with thermostatic mixing valves that meet the NHS Model Engineering Specification D08 and NHS Estates - TMV manufacturers TMV3 performance standards of thermostatic protection.

TMV3 valves are designed and tested to offer improved thermal performance including faster failsafe function and improved control when the TMV3 is subject to variable water flow and temperature fluctuation, whereas TMV2 valves offer a lower standard of thermal performance and are suitable for use in most domestic properties and under some circumstances, sheltered housing accommodation. 


How often should TMV3 valves be serviced?


In health and social care settings, TMV3 valves must undergo regular in-service tests to ensure they perform correctly. If a valve fails, it must either be serviced in accordance with the manufacturer's instructions, or if it cannot be serviced it should be replaced. 

If the manufacturers instructions are unavailable then servicing should follow the guidance given in the NHS Model Engineering Specification D08 which states that the first in-service TMV test must take place between 6 and 8 weeks after commissioning, with a further after 12 to 15 weeks.

Regular on-going in-service tests should be carried out to demonstrate adequate thermal performance is being maintained at the TMV3.




Maintenance is a vital part of keeping TMV’s safe, and the schedule determined by your risk assessment must be followed in order to stay compliant. Valves need to be checked on at least an annual basis or at a frequency determined by the risk assessment. It is important to ensure the valves are working correctly and will offer protection against scalding. Tasks to keep TMV’s safe include:  


  • Temperature Control

To ensure safe, accurate and reliable temperature control is achieved and maintained at water outlets (baths, showers & taps) in accordance with health and safety standards. 


  • Water Quality Standards

Maintaining the appropriate water quality standards and flow rates with regular cleaning, descaling and disinfection of the TMV valve components.


  • Failsafe Operation

Ensuring that the TMV failsafe mechanisms operate and function properly to protect users. 


  • TMV Specification

Review all TMV’s to ensure that the correct specification valves are installed.


  • Record Keeping

All TMV maintenance, inspections and services must be recorded. 


Regular flushing of showers and taps should also be carried out as well. 

Outlets that are used less frequently need to be flushed for several minutes on a weekly basis. Any missed flushing could result in a potentially hazardous increase of bacteria. In premises with people who are at high risk, for example care homes, flushing may need to be done more frequently. This will be determined by a risk assessment.


SMS Environmental TMV servicing solutions are delivered by experienced water treatment and engineering experts using the latest testing equipment and high performance disinfectants to ensure TMVs are maintained, serviced and tested regularly to ensure their correct operation in line with industry recognised guidance.

Our engineering support capabilities allow us to offer a range of expert services including the installation and replacement of thermostatic mixing valves, TMV servicing (including valve and fine mesh strainer cleaning, descaling and disinfection), temperature monitoring and failsafe testing to ensure good water quality standards, safe water temperatures as well as ensuring health and safety standards are achieved and maintained. 

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