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for IE: the current edition of I.S. 813 Domestic Gas Installations.
The sealed primary circuits may be filled or replenished by means of a
temporary connection between the circuit and a supply pipe, provided a
"Listed" double check valve or some other no less effective backflow
prevention device is permanently connected at the inlet to the circuit and
the temporary connection is removed after use.
When the optional permanent filling link is fitted it is not necessary to
remove any part of it after filling or re-pressurising.
5 Before installation
34