Safety valve setting (bar)
3.0
Initial system pressure (bar)
1.0
1.5
Total water content of system
VESSEL VOLUME (L)
litres
25
2.7
3.9
50
5.4
7.8
100
10.9
15.6
125
13.6
19.5
150
16.3
23.4
175
19.1
27.3
200
21.8
31.2
225
24.5
35.1
250
27.2
39.0
275
30.0
42.9
300
32.7
46.8
325
35.7
50.7
350
38.1
54.6
375
40.9
58.5
400
43.6
62.4
425
46.3
66.3
450
49.0
70.2
475
51.8
74.1
500
54.5
78.0
For system volumes other than
those given above, multiply
0.109
0.156
the system volume by the factor
across
13
fig. 9
GW 402/0
3.7.4 Pressure gauge
This is factory fitted to the boiler and
indicates the primary circuit pressure
to facilitate filling and testing.
3.7.5 Expansion vessel
An expansion vessel is incorporated
into the boiler suitable for a sealed
heating system with a maximum water
contents of 135 litres.
If the nominal capacity of the built-in
expansion vessel is not sufficient for
the heating system (for instance in
case of modernization of old open
systems) an additional expansion ves-
sel can be installed external to the boi-
ler in the return pipe as close as pos-
sible to the boiler in accordance with
BS 5449: Part 1.
Guidance on the sizing of an addi-
tional expansion vessel is given in
Table 2.
3.7.6 Circulating pump
The circulating pump is included in the
boiler. The pump head available for
the heating system is shown in fig. 9.
3.7.7 System by-pass
An automatic system by-pass is inclu-
ded within the boiler. The boiler is
suitable for use in systems with
thermostatic radiator valves and no
additional by-pass is required.
3.7.8 Venting
The boiler is fitted with an automatic
air vent. Additional provision should
be made to enable the heating system
to be vented during filling and com-
missioning either by automatic air
vents or manually.
3.7.9 DHW expansion vessel
accessory
A DHW expansion vessel kit (Accy.
No. 8070) is available as an optional
extra from Vaillant Ltd. This expansion
vessel kit should be fitted to the boiler
whenever either a stop valve of the
loose jumper type or a non return
valve are present in the cold water
mains supply to the boiler (fig. 10).
Table 2: Sizing of Additional Expansion Vessel
fig. 10
GW 494/0
