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4.0 System Details
10
4.8
System Filling and Pressurising
1. A filling point connection on the central heating
return pipework must be provided to facilitate initial
filling and pressurising and also any subsequent
water loss replacement/refilling.
2. The filling method adopted must be in
accordance with all relevant water supply bye-laws
and use approved equipment.
3. Your attention is drawn to: IRN 302 and Byelaw
14.
4. The sealed primary circuits may be filled or
replenished by means of a temporary connection
(Filling Loop) between the circuit and a supply
pipe, provided a WRC approved 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
(Filling Loop) is removed after use (Fig. 5).
4.9
Expansion Vessel
1. The appliance expansion vessel is pre-charged
to 1 bar (10 lb/in
2
). Therefore, the minimum cold fill
pressure is 1 bar. The vessel is suitable for correct
operation for system capacities up to 125 litres
(27.5gal). For greater system capacities an
additional expansion vessel must be fitted - refer to
BS 7074 Pt 1.
4.10
Pressure Relief Valve
(Figs. 6 & 7)
1. The pressure relief valve is set at 3 bar,
therefore all pipework, fittings, etc. should be
suitable for pressures in excess of 3 bar.
2. The pressure relief discharge pipe should be not
less than 15mm dia, run continuously downward,
and discharge outside the building, preferably over
a drain. It should be routed in such a manner that
no hazard occurs to occupants or causes damage
to wiring or electrical components. The end of the
pipe should terminate facing down and towards the
wall.
3. The discharge must not be above a window,
entrance or other public access. Consideration
must be given to the possibility that under fault
conditions boiling water/steam could discharge
from the pipe.
4. The pressure relief valve must not be used for
draining the system/boiler.
Discharge Pipe
Fig. 5
Stop Valve
Double
Check
Valve
Mains
CH
Return
Filling Loop
Fig. 7
Fig. 6
Pressure Relief Valve
