Technical data

INSTALLATION & SERVICING INSTRUCTIONS
Some Water Authorities require a stop cock in the cold feed pipe, in which case, a combined feed and
vent cannot be used. A close coupled feed and vent should then be used, taking note of the vent
lengths required to prevent pump surges causing either pumping over or air to be drawn in. The vent
must be at least 22mm diameter and the feed at least 15mm diameter. There must be no valves or
restrictions between the boiler and the outlet of the vent with any system. The feed and expansion
cistern should be not less than 23 litre (5 gallon) capacity, and should not be situated more than 30
metres (100ft) above the boiler.
5.3 Sealed Systems Only
A schematic layout is shown in
Figure 7 .
Safety Valve
A spring loaded safety valve complying with the relevant requirements of BS6759, Part 1, 1984, should
be fitted, and should be preset to operate at 3 bar (44 lbf/in2). It should be positioned in the flow pipe
close to the boiler with no valves or restrictions between the safety valve and the boiler. The safety
valve should be positioned, or any discharge pipe so arranged, that discharge of water or steam
cannot create a hazard to occupants, or damage electrical components or wiring.
Expansion Vessel
A diaphragm type expansion vessel, complying with the requirements of BS4814, 1990, should be
connected at a point close to the inlet side of the pump, in the flow pipe from the boiler. The vessel
should be chosen to suit the volume of water in the system and the charge pressure, which should not
be less than the static head at the point of connection. Further details can be obtained from
"Specification for Domestic Hot Wet Central Heating," published by British Gas.
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