Features

• Expansion vessel with fixed membrane for domestic hot water systems
• Carbon steel body with white epoxy polyester paint finish and stainless steel flange
• Pre-charged to 4.1 bar
• Dimensions: Height 237mm x Diameter 125mm
  
• Max. system temperature: 99ºC
• Max. pressure of vessel: 10 bar
• Connection: 1/2"

The use of an expansion vessel with a water heater of 15 litres or less is optional. However, there are some instances when it is recommended to include an expansion vessel.

An expansion vessel is used to absorb pressure when the water in a water heater heats up and expands. With water heaters below 15 litres, this water expansion is often absorbed by the mains cold feed pipe. However, obstructions on the pipework (such as a check valve, stop cock, pressure reducing valve, etc) can prevent expansion from being absorbed this way. Thus, an expansion vessel is needed.

Essentially, if there is an obstruction 2.8 metres from a 10-litre water heater or 4.2 metres from a 15-litre water heater, the KIT A Expansion Vessel and Check Valve is recommended. Otherwise, the extra pressure will make the safety valve/pressure relief valve discharge and risk overheating the water heater's thermostat.