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Pressure Relief valve
This is the most important safety device. All unvented water heaters must be fitted with a Pressure
Relief Valve (Expansion valve) with a setting of 6 bars.
Pressure Reducing Valve
The cold water supply pressure must not exceed 3.5 bar. If the supply pressure is higher than this
then a pressure reducing valve should be fitted.
Expansion vessel
Expansion must be accommodated using an Expansion Vessel. The Expansion vessel must be
sized to accommodate the maximum expansion of the system and should be suitable for use with
potable water. The size of the expansion vessel is proportional to the volume of the DHW system.
The size of the vessel should be carefully calculated.
A rule of thumb for systems with a cold water supply pressure of 3.5 bars and a maximum heating
temperature of 60°C is that the volume of the expansion vessel should be at least 10% of the total
DHW system volume.
Backflow Prevention
To ensure all expansion takes place in the vessel, a Non Return Valve must be fitted on the cold wa-
ter supply.
Anti Vacuum Valve
The Anti Vacuum Valve is installed to ensure that the water heater is vented and cannot collapse if
exposed to an internal negative pressure.
Mixing Valve
The mixing valve limits the temperature of the delivered water by mixing it with cold water as re-
quired. The delivered water temperature should not exceed 50°C.
Failure to fit these essential safety devices will invalidate the warranty and
create a dangerous installation. This may lead to property damage, injury or
loss of life.
