Some additional advise for ULTRAMIX mixing valve installation

Points requiring special attention

The precision, sensitivity and long service life of the mixing valve will be ensured only insofar as it is properly maintained and if it is correctly chosen beforehand.

In order to define the size of the mixing valve which is best adapted to a given installation, it is absolutely necessary to know two elements : the total instantaneous flow rate, and the dynamic pressure available to the flow for the hot and cold water, at the mixing valve's inlets.

It can be measured or calculated, by using the DARIES Chart or the WATTS software package, which is designed to validate the calculation carried out manually in order to choose the right mixing valve (according to pressures, pipe diameters, desired flow rate and number of points of use).
In no case should you permit static pressure greater than 10 bars.

The proper dimensioning of the mixing valve, that is, the choice of flow rate (according to the data in our technical leaflets).

The hot water temperature which must not exceed 85°C in order to avoid premature aging of the equipment and the installation, but must remain higher than the set point with a difference of 5°C between the two fluids.

The meter for the main water supply, whose given maximum flow rate determines the installation’s possible flow rate.

The length and diameter of the piping which, through pressure losses and water speed, will facilitate or complicate the installation’s operation.

For this reason, the diameter of the inlet pipes (Hot and Cold) and the outlet pipe diameter for mixed water departure, must be the same nominal diameter (DN) as the mixing valve, a difference of one diameter DN (in more or less) is only tolerated.

Scald protection : To prevent scalding, the hot water is instantly cut if the cold water supply is interrupted
(Delta T hot water/mixed water > 10°C).

Pressure loss

Pressure loss is the consumption of the available pressure. Each equipment item (mixing valve, hose-spray assembly, pipe, elbow, ...) consumes a part of the available pressure.

This consumption varies according to the flowrate, hence the supply of pressure loss curves by manufacturers.
Thus, the pressure loss of a mixing valve varies considerably according to whether drawing up or looping is involved. In an installation, one always adds the total of the pressure losses which it contains, in order to verify that the residual pressure will always be equal or superior to 1 bar.

Average :
Mixing valve : 0.8 bars, free ;
0.4 bars, in looping.
Hose-spray assembly: 0.4 bars.


At the entrance of a building or house, the water pressure fluctuates between 3 and 5 bars ; generally,
one assumes a pressure of 3 bars.

Whether or not it is equipped with a thermostatic mixing valve, a good installation must have balanced pressures on both fluids.

WATTS Eurotherm manufactures a complete range of pressure reducing valve for this purpose.
WATTS Eurotherm recommends a service pressure of less than 10 bars and, if possible, between 2 and 4 bars.

Minimum service pressure :__________________0.5 bars

Pressure difference between hot and cold :_______1.5 bars

Installation with time-delay taps

• Check that the time-delay is the right quality and does not cause water-hammers (closing which is too abrupt).

• In case of a water-hammer, the membrane may be damaged, causing the regulation to stop (the mixing valve is then impossible to adjust).

Installation with a circulation loop

• To operate properly with a WATTS Eurotherm mixing valve, a looping must include the following elements :

- A circulating pump

This pump must be properly calculated: temperature drop of 5°C between the mixing valve outlet and return.
(1 m per 100 m of piping). The average manometric head noted in the recirculating pumps with the WATTS Eurotherm system is 4.50 to 6 m for six renewals/hour of the installation’s total capacity.

- A maximum speed of 2 m/sec, particularly after the points of use on the return.

- The return pipe diameter must not be less than that of the mixed water outlet by more than two sizes.

- Two micrometric adjustment valves.

- Four non-return valves : two installed normally on the cold water inlet of the hot water production and the mixing valve + two installed after the micrometric valves on the loop return.

- A water-hammer arrester, in case time-delay taps are used.

- The mixed water return must absolutely be sent back at two points :

- Approximately 80% of the flow on the cold water pipe of the mixing valve ;

- Approximately 20% of the flow to the cold water inlet of the water production or on the storage medium if there is a connecting point. Adjustment to be completed according to temperature drops.

• Maintenance operations.

Temperature Adjustment with a circulation loop
1. Turn off recirculation pump.
2. Open enough points of use on the mixed pipe to meet the minimum flow requirement of the thermostatic mixing valve.
3. Turn temperature adjustment to decrease or to increase the mixed outlet temperature.
NOTE: Please allow valve temperature to stabilize before making your next adjustment. Watts Industries recommends that a temperature gauge is installed on the mixed line and be checked at least monthly under normal flow conditions. The gauge must be installed at least 1,8 meter away from the thermostatic mixing valve.
4. When desired temperature is set, tighten the handle. Turn recirculation pump back on. Close open points of use.

Maintenance of a WATTS Eurotherm mixing valve

- Lubricate the control pins. Check and eventually replace the O-rings every 18 months.

- Brush, clean the cartridge and remove the scale every :

- 18 months for a 14 °DH

- 12 months for a 18 °DH

- 6 months for a 22 °DH

(NB: 1 °DH = 1,78 French °TH)

- When refitting the cartridge, check the condition of its seat and, if necessary, clean it ;

• Operations subsequent to maintenance or stoppage

- Redo the calibration.

- If the temperature obtained after calibration is not constant, check that the O-rings and filters are at the same height.

- If one of the two water lines does not come in, check that the valve-filters have been refitted in the right direction. The brass cone which acts as a valve stop must be fastened via the top.

- Check that refilling with water has not caused an abrupt influx of sand and other waste matter.
On a model from the previous range, check that the control pin has been refitted.


The operating simplicity of WATTS Eurotherm mixing valves results from their ease of implementation and the unparalleled quality of the result.

The supply must correspond to the desired flowrate or to the diameter of the mixing valve’s inlets.
The WATTS Eurotherm software package or the Daries chart provides all the useful information in a form which is very easy to use. In fact, the water speed must not exceed 2 m/sec. for good acoustic comfort, and 2.5 m/sec. in order to protect the installation from serious risks such as water-hammers.

The hot water storage tank must be sized according to use.

Dynamic pressures (water pressure, tap open) must be 3 bars in order to obtain the best

regulation at the best flowrate (generally, the static pressures which are indicated are higher than the dynamic pressures). The flowrates which appear in the tables or curves are in fact always given for dynamic pressures.
At the same time, they indicate the pressure loss, that is, the dynamic pressure consumption corresponding to these flowrates.

It is necessary to include isolation valves at the inlets and at the outlet of institutional mixing valves.

A WATTS Eurotherm mixing valve operates perfectly with a booster or a circulation loop.

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Technical leaflet