How Thermostatic Mixer Valves Work?

What is a Thermostatic mixing valve?

A Thermostatic Mixing Valve is a device that mix or blends hot water (usually stored at temperatures high enough to kill bacteria) with cold water to ensure constant, safe outlet temperatures preventing scalding.

How a thermostat works:Hot and cold water entering the valve is mixed to a temperature pre-selected by the user or installer. A thermal-sensitive mechanism within the valve’s body automatically proportions the amount of hot and cold water entering to produce the required blend.

The mechanism then automatically compensates for any reasonable variations in supply pressures or temperatures within the design range to maintain the pre-selected temperature. In the event of cold water supply failure, the thermostatic mixing mechanism will automatically shut down the flow to prevent discharge of dangerously hot water.

The flow will also be shut down in the event of a hot water supply failure to prevent thermal shock. In the event of a sudden supply temperature increase (‘spike’), the TMV will quickly (but not absolutely instantly) adapt and deliver water at a safe temperature.

Thermostat Components Explained

Thermostatic mixing element:There’s a temperature sensitive element which expands or contracts depending on the temperature of the water surrounding it. When the thermostatic element senses a temperature change, it moves a piston which changes the proportion of hot and cold water being mixed in the valve. This movement enables the valve to remain stable and to shut down in case of cold or hot water failure.

Piston Component:Usually connected to the thermostatic element, the piston moves back and forth over the cold and hot ports of the valve, changing the proportion of hot and cold water entering the valve depending on the temperature of the water.

Return spring:When the thermostatic element expands it moves the piston under its own energy and compresses the return spring; when the thermostatic element is cooled, the thermostatic element contracts and the return spring pushes the piston back in its original position.

Temperature adjustment:Autotaps thermostatic mixing valves have a temperature adjustment (usually located at the top of the valve). Typically, this can be adjusted to change the position of the piston and therefore the proportion of hot and cold water entering the valve.


Frequently Asked ‘Questions and Answers’

Can problems with ‘non-return valves’ cause the temperature control system to fail?Non-return valves can be held open by dirt or grit. In this case, if the mains pressure and hot water pressure differ, hot water can be forced back down the piping system the wrong way through a non-return valve, meaning the water temperature may no longer be regulated.

There are other factors that can causes a thermostat to fail such as an open vented system, localised expansion from water heater, a failed seal in a non-return valve, a particulate contamination and incorrect plumbing. Correct installation and servicing are also essential to ensure that filtration measures and checks on the product are performed.

Can the heating system influence the performance of TMVs?It is important that the installation method and technical parameters in our instruction booklet is adhered to as failure to do so may prevent the valve from operating correctly.

Common installation errors are:
1. Failure to use flow regulators when installing a thermostatic product to a combi boiler system. This may cause performance issues during winter months.
2. Failure to remove flow regulators when installing to a vented system, i.e. a traditional immersion heater. This may reduce the water flow.

What's the difference between ATV-9004C and ATV-9004B?

They're litterally both the same thing, except for only one difference.
ATV-9004B has a 'wall-mounting' brackets attached to it, while ATV-9004C has a 'female' connection end, which can be connected directly to a control box water 'inlet' supply.