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3.2.4 Air Vents
The plastic plug of the automatic air vent factory-fitted to the appliance must be loosened when
filling the system in order to bleed the air from the appliance. Retighten the plastic plug once the
system has been correctly filled and vented. In addition to any factory fitted air vents it is
recommended that another air vent is fitted at the highest point in the system. Where the flow
pipework drops down from the appliance the installer must ensure that an automatic air vent is
fitted to the top of the pipework to prevent air being trapped in the appliance.
3.2.5 Drain Cock
A factory-fitted drain cock is fitted to the return pipe of the appliance, However drain cocks
should also be fitted to the lowest points in the system to allow the system to be completely
drained.
It is recommended that a means of isolating the flow and return pipework to the appliance
should be provided as part of the installation. Methods of ensuring that such isolators cannot be
accidently left in an undesired position should be used in order to prevent the inadvertent
isolation of the appliance or restriction of the flow and return system water to the appliance.
3.2.6 Pipework
We strongly advise that all installation pipework is run in copper. However, if plastic pipe is used
the last 1000mm of pipework connected directly to the appliance must be of copper. All
connections to the appliance must be made with compression fittings.
3.2.7 Heating System Design
The heating system must be designed for a fully pumped appliance.
3.3 Sealed Systems
3.3.1 Expansion Vessel (WS 18 Models only)
The WS18 appliance is supplied with a 24 litre expansion vessel charged to 1.0 bar. This can
accommodate a maximum combined appliance and system volume of 210 litres. If these
maximum total system volumes are to be exceeded, additional expansion capacity will be
required. Refer to BS7074: PART 1, BS EN 12828, BS EN 12831 and BS EN 14336 for details
of expansion vessel sizing. The values given in the Table 7 below are for total system volumes
which include the water capacity of the appliance which can be found in Table 1: Product Data
(See page 6).
The WP18 appliance is not supplied with an expansion vessel and if connected to a sealed
system, an expansion vessel must be fitted and sized according to Table 7 below.
INITIAL
CHARGE
(bar)
2.1
0.5
2.7
1.0
2.9
1.5
TOTAL
SYSTEM
25
VOLUME
(Litres)
4.2
6.3
8.3
5.4
8.2
10.9
7.8
11.7
15.6
50
75
100
Table 7: Expansion Vessel Volumes
VESSEL VOLUMES (Litres)
10.5
12.5
14.6
13.6
16.3
19.1
19.5
23.4
27.3
125
150
175
42
16.7
18.7
20.8
21.8
24.5
27.2
31.2
35.1
39.0
200
225
250
22.9
25.0
30.0
32.7
42.9
46.8
275
300
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