Technical data

Page 71
10.2 Sealed Systems
10.2.1 Expansion Vessel
Refer to BS7074: PART 1 and BS5449 for details of expansion vessel sizing. The values given
in the table below are for total system volumes which include the primary water capacity of the
boiler which can be found in the Technical Data section of this manual. System and Combi
models up to 120HE are supplied with a 12 litre expansion vessel charged to 1.0 bar. This can
accommodate a maximum combined boiler and system volume of 110 litres. Where permitted
by the type, size and configuration of heating system the expansion vessel bladder pre-charge
pressure can be reduced, prior to filling the system, to 0.5 bar in order to accommodate a total
system volume of 145 litres. If these maximum total system volumes are to be exceeded,
additional expansion capacity will be required.
INITIAL
CHARGE
VESSEL VOLUMES
0.5
2.1
4.2
6.3
8.3
10.5
12.5
14.6
16.7
18.7
20.8
22.9
25.0
1.0
2.7
5.4
8.2
10.9
13.6
16.3
19.1
21.8
24.5
27.2
30.0
32.7
1.5
2.9
7.8
11.7
15.6
19.5
23.4
27.3
31.2
35.1
39.0
42.9
46.8
SYSTEM
VOLUME
25
50
75
100
125
150
175
200
225
250
275
300
When measuring the expansion vessel bladder pre-charge pressure, using a tyre gauge, the
system should be cold and the system pressure should be relieved (by manually operating the
system pressure relief valve) in order to obtain an accurate reading.
10.2.2 System Filling
For all System and Combi boilers a filling point complete with a filling loop is supplied fitted to
the expansion vessel. The filling loop must be disconnected from the mains supply after filling.
A system pressure when cold of 1 bar is recommended. After filling, vent all air from the system.
The plastic plugs of the auto air vent(s) factory fitted to the boiler must be loosened when filling
the system in order to bleed the air from the boiler.
10.2.3 System Pressure
Water loss from the system as indicated by a reduction in pressure on the pressure gauge may
be made up through the filling loop. In the first week of operation it is normal to see a drop in
system pressure. After this time the system pressure must be rechecked and the system
refilled. Failure to do so may lead to boiler faults.
Special attention must be given to the concentration of corrosion inhibitors in the system water
where there is a need for topping up or refilling. Inhibitor concentrations must be restored to the
concentrations specified by the inhibitor manufacturer.
Frequent or routine refilling and topping up of the system should not be necessary on an
ongoing basis and may prove harmful to the appliance. Should topping up prove necessary on a
frequent or routine basis you must contact Warmflow or your installer.
10.2.4 Pressure relief Valve
Any pressure relief valve fitted to the boiler or system must be able to discharge externally to a
drain where the discharge can be seen but cannot cause any injury or damage. No other valves
should be positioned between the relief valve and discharge termination.