How to Install the Mixing Valve | Circoflo | Underfloor Heating Your Way

How to Install the Mixing Valve

This guide will show you how to setup the centralised mixing unit.


The central mixing unit is a safety device to stop high temperature water from entering the underfloor heating system. Water hotter than 60˚C must never be used in the underfloor heating system. If the heat source can provide water at a temperature greater than 60˚C it is advised than a central mixing unit is used. The water must be clean and treated before installation of the mixing unit.

The maximum underfloor heating area using a Circoflo system is 200m2. If larger areas need to be served then multiple units can be installed.

We advise that strainers are installed in the system to prevent debris from entering the mixing unit and underfloor heating pipe. Also, if the water is very hard in the area then installation of a scale reducer is recommended.

What is Supplied

Please check all components are present before assembly:

  • Mixing valve with a temperature range from 30˚C to 60˚C (1). The mixing valve has 1 ½” connections (2) and (9) for a circulator (not supplied) and three ¾” to 22mm compression adaptors (8) (supplied).
  • Elbow with 1 ½” connection for circulator and a ¾” to 22mm compression adaptor. The elbow has a socket for the temperature gauge (9).
  • Temperature gauge to insert into the socket in the elbow for displaying the mixed water temperature (6).
  • Four ¾” to 22mm compression adaptors (8)

What is not supplied
  • You will also need a standard domestic circulator, we recommend one with 6m head. If the system pressure drop requires a higher performance circulator then this can be installed. The circulator (and boiler) will be switched from the Circoflo controls.
  • Connecting pipe work and fittings
  • Isolating valves

  • The central mixing unit can be sited anywhere on the primary  before the underfloor heating manifolds.
  • The mixing unit can be installed in either a horizontal or vertical position, however consideration must be given to the circulator manufacturer’s instructions.
  • The connections on the mixing unit are shown:

H = HOT (High temperature connection from the boiler) (4)

C = COLD (Return from the underfloor heating and to the boiler)  (5) from UFH (3) to boiler

MIX = Mixed water outlet with water at the correct temperature for the underfloor heating (7)

  • Adaptors are provided for 22mm compression connection Please ensure that the pipe work and mixing unit is properly supported.
  • Isolation valves and a bypass to be fitted as required depending on the boiler and system setup.
  • Ensure that the system is free from debris. We recommend that strainers are installed to prevent debris from entering the mixing unit.
  • With the mixing unit installed and connected to the primary pipework and the circulator fitted (not supplied) the mixing valve can be set to the required temperature. This is done by partially unscrewing the mixing valve knob screw (1) and turning the knob clockwise to reduce the water temperature and anti-clockwise to increase the water temperature. The settings and corresponding temperatures from the table below are approximate. The temperature should be checked on the temperature gauge (6) (wait for the temperature to settle) and the setting adjusted to achieve the desired flow water temperature. The temperature gauges at each manifold should also be checked, if there a drop in water temperature then the setting at the mixing valve should be increased.
  • The water temperature going into the underfloor heating pipe should never exceed 60˚C and should not be set for continuous running higher than 55˚C.
  • The valve is pre-set to 45˚C. This may be too low for some underfloor heating systems.



















 All temperatures approximate

  • Once the temperature has been set, tighten the screw (1) to lock the setting.
  • Check the mixed temperature from time-to-time to ensure that the system is operating as it should.


The mixed water temperature is too low 

  • Check the that the temperature from the heat source is high enough
  • This should be at least a few degrees higher than the required mixed water temperature.
  • Check that the mixing unit is operating properly, debris in the unit will cause the mixing valve not to open and close properly.

Underfloor is not working but mixed water temperature is correct

  • Check the circulator at the mixing unit is operating.
  • Check the thermostat and actuator valve at the manifold is working correctly, if not check the wiring and thermostat program – see manifold and thermostat instructions
  • Make sure the underfloor heating circuits are balanced.
  • If the water temperature is too low at the manifold then increase the mixing valve setting. Flow and return pipe to the manifold may have to be lagged if the temperature drop is too high.
  • If the manifold is located far from the mixing unit the pressure drop may be too high, in this case a larger capacity pump may be needed.

Circulator not working

  • Check the switched power supply for the circulator from the Circoflo control system is correct. The circulator (and boiler) should activate when there is a call for heat from a thermostat.

Technical Information
  • Temperature range 30˚C to 60˚C
  • Maximum working temperature 90˚C
  • Factory pre-set 45˚C
  • Maximum static pressure 10 bar
  • Suitable fluid: Max 50% glycol