GENERAL
mini HE
--- Installation & Servicing
11
Table 5
System charge pressure
(bar)
0.5
0.7
1.0
Safety valve setting
3.0
Vessel pre---charge pressure
(bar)
0.7
System volume (litres)
Volume of expansion vessel
in addition to 6 litre unit
fitted to boiler
75
---
---
---
100
0.3
0.8
1.4
125
1.8
2.5
3.2
150
3.4
4.2
5.0
175
5.0
6.0
7.0
200
6.5
7.6
8.7
225
8.1
9.3
10.6
250
9.6
11.1
12.4
275
11.2
12.8
14.3
300
12.8
14.5
16.1
Multiply this factor by
system volume and deduct
6 litres to obtain size of
additional vessel for other
system volumes.
0.063
0.069
0.074
5 Size of expansion vessel
For the system water expansion to be contained by the
6
litre
expansion vessel the cold system volume must not exceed:
96 litres when pressurised to 0.5 bar (cold)
88 litres when pressurised to 0.7 bar (cold)
81 litres when pressurised to 1.0 bar (cold)
If the pressure exceeds 2.65 bar when the boiler is up to
temperature with all radiators in use then an additional
expansion vessel MUST be installed on the return pipework.
For expansion volumes see Table 5.
Guidance on vessel sizing is given in BS 7074:1 and BS 5449
For IE refer to the current edition of I.S. 813.
6 Hydraulic Loss
Remaining pump capacity
0
1
2
3
4
5
6
0
200
400
600
800
1000
1200
1400
Flow rate l/hour
m H2O
7 Draining the system
Draining taps MUST be located in accessible positions to
permit the draining of the whole central heating system,
including the central heating side of the boiler. The taps
should be at least 1/2” BSP nominal size and be in
accordance with BS 2879.