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SYSTEM DESIGN AND PLANNING INFOrMATION
4.0
(f)
central heating circuit expansion vessel
The seven litre appliance expansion vessel (see figure .a) is supplied pre-charged
to 1.0 bar. Therefore the minimum cold fill pressure should be 1.0bar. The vessel is
suitable for the correct operation of central heating system capacities up to 70 litres.
For greater system capacities an additional expansion vessel must be fitted (as shown
in Figure 4.1). For guidance, the expansion vessel volumes are given in Table 4.1
In GB: The expansion vessel must conform to the current issues of BS4814 and
BS7074 Parts 1 and . It must be connected to the central heating return pipe and
sized according to BS5449 and BS7074 Part 1.
In IE: Refer to the current edition of I.S. 813.
Table 4.1 - Expansion vessel volume required
Safety Valve Setting (bar)
Vessel Charge Pressure (bar)
Initial (cold) Fill Pressure (bar)
Total System Capacity (l)
5
50
75
100
15
150
(g)
Pressure relief valve/discharge pipe
A non-adjustable system safety valve set at 3 bar is fitted
to the appliance (figure 4.5). All discharge pipework,
fittings, etc should be suitable for pressures greater than
3 bar and temperatures greater than 100ºC.
The pressure relief discharge pipe should not be less than
15mm diameter. It should run continuously downwards
and discharge outside the building, preferably at low
level over a drain. It should be routed and terminated in
such a way that no hazard occurs to people or damage
is caused to wiring or electrical components. The end of
the pipe should terminate facing down and towards the
wall (or be provided with a suitable guard).
The discharge must not be above a window, or
other public access way. When choosing a location
consideration should always be given to the possibility
that boiling water/steam could discharge from this
pipe.
(H) Pump characteristics
The boiler is fitted with a modulating Grundfos UPR 15-
60 pump. The pump operates at maximum speed when
in the boiler is in DHW mode and modulates when the
boiler is in the central heating mode.
The pressure flow characteristics of the pump (available
for the central heating circuit) are shown in figure 4.6.
0.5
0.5
1.0
1.5
.0
Expansion Vessel Volume (litres)
.1
3.5
6.5
13.7
4.
7.0
1.9
7.5
6.3
10.5
19.4
41.3
8.3
14.0
5.9
55.1
10.4
17.5
3.4
68.9
1.5
1.0
38.8
8.6
Figure 4.5
Figure 4.6 - Pump characteristics
3.0
1.0
1.5
1.0
1.5
.0
1.5
.7
4.7
10.3
3.9
5.4
9.5
0.6
7.8
8.
14.
30.9
11.7
10.9
19.0
41.
15.6
13.6
3.7
51.5
19.5
16.3
8.6
61.8
3.4
Page 17
.0
8.3
16.5
4.8
33.1
41.3
49.6
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