Thermostatic mixing anti-scald valve

Water temperature is a very important factor in the bathing experience, not only for comfort but for safety reasons too. The ideal water temperature for most people falls between 35°c and 38°c.

If you have an anti-scald valve on your bathtub, then it is likely that this setting is already set to the right range but any hotter than this can cause discomfort or even injury.

If your bath seems to be running too hot and you need to adjust your anti-scald valve, there are some things you should know first.

What is a Scald?

A scald occurs when an individual has been immersed or splashed with hot liquid or steam. The resulting injury from heat transfer into the skin and underlying tissue of the body is called a scald.

Scalds can happen very quickly and be caused by a number of things such as the hot water coming out of taps at home through to the steam from boiling your potatoes or your kettle.

These injuries are serious and many people in the UK suffer from them. Due to the serious nature of scalding, many bathtubs are fitted with an anti-scald valve.

What is an Anti-Scald Valve?

An anti-scald valve is a valve that has been designed to prevent you from being scalded by ensuring that water does not exceed a certain temperature, therefore, removing the risk of injury or discomfort to the user.

If your bathtub has one of these valves installed it will be near the hot and cold-water supply in the bathtub or shower.

There are 2 main types of anti-scald valves, and they are pressure balanced valves and thermostatic mixing valves.

Pressure Balanced Valve

Pressure balanced valves work by adjusting the water flow depending on the pressure and to do this adequately the valve needs to be calibrated to the correct temperature setting.

The valve works by limiting the flow of hot water to a tap depending on the pressure of the cold water. For example, if the cold tap is used downstairs and the water pressure drops, the piston moves to slow the flow of hot water to compensate.

The problem with this type of valve is that each time there is a change in water temperature for any reason i.e., the boiler servicing etc. then the valve needs recalibrating.

Thermostatic Mixing Valve

Thermostatic mixing valves are a little more expensive than pressure balanced valves and they are of better quality too.

TMV’s regulate the flow of water based on the temperature within the mixing chamber. This means that the heat can be set and regardless of water pressure, the internal thermostat will ensure that the water output is at the desired temperature.

Are Anti-Scald Valves a Legal Requirement?

Having anti-scald valves in the UK is not a legal requirement per se but, since 2010 they have been made a requirement in all new building developments.

The regulations state: “The hot water supply to any fixed bath must be so designed and installed as to incorporate measures to ensure that the temperature of the water that can be delivered to that bath does not exceed 48˚C.” Full regulations can be found here.

How to Adjust an Anti-Scald Valve?

If you have found that your anti-scald valve is set too high and the temperature is still too hot, it can be adjusted. The same goes for if you feel that the temperature is a little too cold. Luckily, with a small adjustment, you will be able to enjoy your soak at the perfect temperature again.

Step 1 – Check the Water Temperature on Your Boiler

Firstly, if you have a combi boiler installed, there will usually be a digital dial that you can use to adjust the temperature. This dial will enable you to increase and decrease the water temperature before it even reaches your bathtub.

The reason for checking the boiler first is because you may not have an anti-scald valve fitted under your bathtub.

Step 2 – Locate the Anti-Scald Valve

The anti-scald valve will usually be located behind the bath panel but depending on the design of your bathroom, it may be somewhere else close as the building regs state:

“The length of supply pipes between in-line blending valves and outlets should be kept to a minimum.” – Building Regulations 2010, Sanitation, Hot Water Safety and Water Efficiency (sec G3.68).

Step 3 – Remove Anti-Scald Valve Cap

TMV’s will have a central cap and in most cases, this cap will need to be removed to reveal the nut for opening and closing the valve.

The cap will usually be held on by a small central screw, if not, it may just pop off.

Step 4 – Adjust the Valve

To adjust the water temperature, using a spanner, turn the nut until you reach your desired level. Turning clockwise will make the water colder and turning anticlockwise makes the water warmer.

Why Might You Need to Adjust the TMV?

The regulations state that water should not be hotter than 48°c. Many TMV’s are set at manufacture to 43°c so, if you have recently had one installed, it may not have been set high enough for you.

Alternately, the anti-scald valve may be expelling water that is far too hot and you may need to cool it down a little if you have young children.

Conclusion

Adjusting your anti-scald valve is an easy task to do but remember that they are there for a reason.

They are there to regulate your water temperature to prevent scaldings that occur with scary regularity.

If you really do need to adjust your anti-scald valve in your own home, do so at your own risk – if you are attempting to adjust a valve in your workplace, I would check your company policies before doing anything as you could land yourself in hot water!

Did You Know?

“It only takes 1 second to get a deep burn from hot water at 60°c!”*

“2,000 children a year attend A&E following bath water scalds – That’s 5 children EVERY DAY!”*

“Greatest number of paediatric burn patients are infants and toddlers younger than 3 years of age burned by scalding liquids!”**

“Hot tap water burns cause more deaths and hospitalisations than burns from any other hot liquids!”**

*hotwaterburns.org
**stanfordchildrens.org

Frequently Asked Questions

Are anti-scald valves required?

In the 2010 update of the new building regulations, anti-scald valves have been made a requirement in all newly built property although they are not deemed as required in houses built prior to 2010 although they are strongly recommended.

Can you adjust a thermostatic mixing valve?

Yes, thermostatic mixing valves (TMV’s) can be adjusted by removing the central cap. Using a small spanner, turn the valve anticlockwise to increase the temperature and clockwise to decrease it.

Can I remove anti-scald valve?

If you own your home, you can remove the anti-scald valve although I am not sure why you would want to. Anti-scald valves were introduced in the 2010 update of the building regulations for a reason.

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