Water Supply Industry Interpretations and Advice

  • Area of Interest : Backflow prevention
  • Topic : Filling loops
  • Title : Rapid filling of heating and cooling systems in non-domestic premises
  • Clause Reference : Schedule 2 paragraph 24 & G24.2
  • Reference Number : B09
  • Decision Date : October 2001 (Revised May 2004)

When vented or unvented closed circuit heating or chilled water cooling systems require rapid filling for the purpose of flushing or initial filling after installation, a temporary flexible filling loop connection from a supply pipe with backflow protection may be used providing that:-

  1. the section of pipe being filled contains no fluids, or
  2. the section of pipe being filled contains a heat transfer fluid that contain no additives or is a fluid of no greater risk than fluid category 3
The required backflow protection being a double check valve installed on the connection point to the supply pipe, with an optional additional service valve or double check valve installed on the connection to the closed circuit filling point (see diagram R24.2a below also refer to Defra G clause G24.2 a).



The temporary filling loop must be removed after the filling is complete and before the system is pressurised. The same method is permitted for re-filling after complete drain-down of existing systems provided no additives are introduced or already present in the system. Routine topping up of the closed circuit during normal operation must be carried out with the backflow protection required by the Water Supply (Water Fittings) Regulations, Byelaws in Scotland. Where permanently installed arrangements are required for rapid filling, the backflow protection must comply with fluid category four.

(Also see B54 'Disconnection of temporary filling loops' & B22 'Filling and topping up heating system primary circuits')