Water Supply Industry Interpretations and Advice

  • Area of Interest : Installation
  • Topic : Water heaters - expansion water
  • Title : Mains fed water storage heaters of 15 litres or less.
  • Clause Reference : G17.1d
  • Reference Number : I09
  • Decision Date : February 2002

Although it is excluded from the Guidance in G17.1d, manufacturers are advised that a water heater of 15 litres or less capacity, fed from the supply pipe, should be fitted with an approved expansion vessel or approved expansion valve. This is to prevent failure of the heat exchanger because of the inability of expansion water to return to the supply pipe if, as is usual, a check valve is installed upstream.

An Installation and Requirement Note (IRN) will be added to relevant entries in the Water Fittings and Materials Directory.