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The BMA Bathroom Academy CPD | No.4
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Scalding by uncontrolled hot water is deadly serious and following the publication of Revised Part G of the Building Regulations, in future, baths in all new homes must be fitted with a Thermostatic Mixing Valve. This device is designed to prevent scalding by limiting the temperature of hot water.
Hot bath water is responsible for the highest number of fatal injuries in the home. Each year around 20 people die as a result of scalds. A further 570 suffer very serious scalding injuries which can cause disfigurement, for life. Second and third degree burns can result from uncontrolled hot water and the statistics show that the very young and the very old are the most vulnerable.
What is a TMV?
A thermostatic mixing valve is a device which mixes hot and cold water before discharging it at a fixed stable temperature.
TMVs are used in both domestic and commercial situations and particularly in hospitals and care homes where users are most vulnerable. They are used to control water at a safe pre-determined temperature thus minimising the possibility of anyone sustaining a serious scald injury.
How does a TMV work?
Three possible types of mechanism are used to operate a TMV.
• The wax capsule mechanism expands and contracts according to the temperature of the incoming water and thus, via the valve’s ‘shuttle’ system, will maintain a stable temperature of the outgoing water.
• The bi-metallic coil mechanism also reacts to temperature changes of incoming water and adjusts the proportion of hot and cold to maintain a stable temperature.
• The electronic/digital TMV uses a system of motorised pumps and valves to control the outgoing water temperature.
What do they look like?
TMVs come in a variety of designs.
• T-pattern valves are typically situated under the washbasin or bath to control the temperature of the outgoing water.
• TMVs may be found within the body of the mixer tap itself.
• TMVs are most commonly used in shower controls, either sequential or dual control for built-in or exposed models.

What water temperatures are TMVs set to?
Temperature stability is key to the operation of TMVs and wherever they are used they must maintain a set mixed hot water temperature of ±2°C.
In order to prevent scalding the TMV must default to shut off in the event that the cold water supply is lost.
BS7942 and NHS D08 show tables which indicate the maximum temperatures relating to different bathroom applications. For example:
• A TMV controlling water to a washbasin or shower should be set at a maximum 41°C
• A TMV controlling water to a bath should have a maximum of 44°C
• A TMV controlling water to a bidet should be set at 38°C.

What factors affect the choice of product?
Many factors affect the final choice of TMV but all of them should comply with the Water Supply (Water Fittings) Regulations 1999 and the Water Bye-Laws Scotland 2000. Also there are a number of British and Industry Standards which cover the performance and safety aspects of TMVs.
TMVs may be approved to the appropriate ‘BuildCert’ Scheme. In domestic situations the valve must comply with the specifications laid down in TMV2 and in the more strict applications of commercial or public buildings TMV3 becomes relevant.
Other factors affect choice. Water Efficiency and ‘Green Issues’ are becoming increasingly important. TMVs also need to match to the existing plumbing system. For instance a TMV designed to work in a high pressure system will not work effectively in a low pressure system. The valve mechanism will not respond to the low pressure water supply, and may even become dangerous.
It is also important the boiler system is considered. A TMV will work well with a combi boiler provided that it is of the ‘fully modulating’ type.

How are TMVs installed and maintained?
The correct installation, commissioning and maintenance of a TMV is critical to its correct operation. Water supplies must be connected correctly – if they become swapped the TMV may fail to do its job and scalding could result.
Supply pipes should be flushed after installation to remove debris and service valves should be installed to allow regular and effective maintenance.
An excellent new publication from the BMA provides an in-depth and informative guide to Thermostatic Mixing Valves. This latest Industry Guide, a valuable resource for anyone in the bathroom industry, offers essential information for the plumber, retailer and merchant. The readable text and excellent images bring home the importance of the TMV.
The guide, in PDF format, is downloadable from the BMA’s Bathroom Academy website www.bathroom-academy.co.uk/guides2.asp and for a nominal fee of £20 you can apply to register for the one-off TMV Guide and CPD Certification. This is an excellent and invaluable way for anyone in the bathrooms industry to bring their knowledge base bang up to date. The guide and certificate is an effective entry to increasing skills and product knowledge and helps readers get one step ahead of their competitors during difficult trading conditions.
TMVs save lives – learn about them.
CPD QUESTIONS

The Bathroom Academy Generic Industry Guide to THERMOSTATIC MIXING VALVES. Downloadable from http://www.bathroom-academy.co.uk/guides2.asp
Answer these 10 questions to gain your Bathroom Academy CPD points
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1 – Give the definition of a TMV? .
2 – Name the three types of TMV mechanism
3 – What type of TMV is most commonly used for a bath?
4 – Name the regulations to which a TMV must comply if an offence is to be avoided.
5 – What should happen in a TMV if the cold water supply is interrupted? And why?
6 – According to BS7942 and NHS D08 what maximum water temperature should a TMV be set at when used with a normal bath?
7 – A TMV designed to work in a high pressure plumbing system will not work correctly in a low pressure system TRUE or FALSE.
8 – What must be carried out to the plumbing system after installation of the TMV?
9 – What happens if, during installation of the TMV, the hot and cold water supplies get swapped, and so what if they are?
10 – A TMV should not be installed with a combi boiler, ever? TRUE or FALSE
MARKING
If you achieve 80% you will gain Bathroom Academy CPD points. Submit your answers by photocopying or cutting out the questions section and returning it marked ‘TMV CPD’ to
The Bathroom Academy, Federation House, Station Road, Stoke-on-Trent, ST4 2RT
Or via email to : info@bathroom-academy.co.uk

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