Installation Guide – Thermostatic Mixing Valves (TMVs)

Installation Guide – Thermostatic Mixing Valves (TMVs)

1. Pre-Installation Requirements

Before installation, confirm that system conditions meet the manufacturer’s specified operating limits:

• Pressure Differential (∆P):
  The pressure difference between hot and cold supplies must not exceed the manufacturer’s stated limits. Excessive differentials are particularly common in systems combining tank-fed and mains-fed supplies and can be difficult to correct once installed.

• Temperature & Pressure Verification:
  Ensure both hot and cold water temperatures and pressures are within the acceptable operating range for the TMV.

Failure to meet these criteria may result in unstable temperature control or valve malfunction.

2. Pipework and System Preparation

Once system conditions are confirmed, the supply infrastructure must be prepared to support correct TMV operation:

• Thoroughly flush all supply pipework prior to installation to remove debris and contaminants.

• Install isolation valves, preferably local to the TMV, to allow for servicing and maintenance.

• Fit inline strainers (normally supplied with the TMV as part of the connection fittings).

• Keep mixed water outlet pipework as short as practicably possible.

• Ensure the manufacturer’s minimum flow rate is achieved during normal operation.

• If flow restriction is required on the mixed outlet, ensure it is positioned so it does not impair TMV performance.

3. Point-of-Use TMV Installation

Point-of-use thermostatic mixing valves must be installed strictly in accordance with the manufacturer’s instructions.

Key considerations:

• Select an accessible installation location to allow regular inspection and maintenance.

• Ensure the installation includes:

  • Local isolation valves

  • Integral or inline strainers

• Minimise the length of blended water pipework downstream of the valve.

For TMVs installed remotely from the outlet, guidance from Health Technical Memorandum (HTM) 04-01, paragraph 9.49, should be followed:

“Pipework containing blended water should be kept to a minimum. Generally, the downstream dead-leg should not exceed 2 m, and the complete length of the spur should not exceed 3 m.”

4. Group Blending TMV Installation

Group blending valves are typically used to supply large volumes of blended water to multiple outlets.

Installation considerations include:

• Valves may be located some distance from outlets; therefore, provisions should be made to control hygiene risks in blended water pipework.

• Modern group blending systems may include automated thermal disinfection, allowing mixed outlet pipework to be periodically sterilised.

• Thermal disinfection is often achieved by electronically controlling secondary pumps and thermostats.

Both conventional group blending TMVs and hybrid valves with integrated disinfection functionality should be installed in accordance with the manufacturer’s schematics and guidance.