© Baxi Heating UK Ltd 2009
3.0 System Details
9
3.6
Sealed Systems
(Fig. 9)
1.
SAFETY VALVE
- A safety valve complying with the
requirements of BS 6283 Part 1 must be fitted close to the
boiler on the flow pipe by means of a horizontal or vertically
upward connection with no intervening valve or restrictions
and should be positioned to facilitate testing. The valve should
be pre-set and non-adjustable to operate at a pressure of 3
bar (45 Ibf/in
2
). It must be arranged to discharge any water or
steam through a pipe to a safe outlet position.
2.
PRESSURE GAUGE
- A pressure gauge of minimum range
0-4 bar (0-60 Ibf/in
2
) with a fill pressure indicator must be
fitted to the system, preferably at the same point as the
expansion vessel in an easily visible position.
3.
EXPANSION VESSEL
- An expansion vessel complying with
the requirements of BS 4814 must be fitted to the system by
means of a connection close to the inlet side of the circulating
pump in accordance with the manufacturers instructions, the
connecting pipe being unrestricted and not less than 15mm (
1
/
2
in) nominal size. The volume of the vessel should be suitable
for the system water content and the nitrogen or air charge
pressure should not be less than the system static head (See
Table. 1).
Further details of sealed system design can be obtained from
BS 5449 and the British Gas publication entitled 'Specifications
for Domestic Wet Central Heating Systems'.
4.
FILLING POINT
- A filling point connection on the central
heating return pipework must be provided to facilitate initial
filling and pressurising and also any subsequent water loss
replacement / refilling.
The sealed primary circuits may be filled or replenished by
means of a temporary connection between the circuit and a
supply pipe, provided a ‘Listed’ double check valve or some
other no less effective backflow prevention device is
permanently connected at the inlet to the circuit and the
temporary connection is removed after use.
The filling method adopted must be in accordance with all
relevant water supply regulations and use approved
equipment.
Your attention is drawn to, for GB: Guidance G24.2 and
recommendation R24.2 of the Water Regulations Guide. for
IE: the current edition of I.S. 813 “Domestic Gas Installations”.
5.
MAKE UP SYSTEM
- A method of replacing water lost from
the system should be provided either by means of a make up
vessel of not more than 3 litres
(5 pints) capacity, mounted above the highest point of the
system, or by pre-pressurisation of the system.
6.
VENTING
- A method of venting the system during filling
and commissioning must be provided by fitting automatic air
vents or by venting manually.
7.
HOT WATER STORAGE
- The hot water storage vessel
must be of the indirect coil type.
8.
SYSTEM COMPONENTS
- All components used in the
system must be suitable for operation at 110°C (230°F) and at
the pressure allowed by the safety valve.
Initial System
Pressure (Bar)
Vessel Charge
Pressure (Bar)
Multiply Total
Water Content Of
System By (Litres)
0.067
0.112
0.207
0.441
0.087
0.152
0.330
0.125
0.265
0.5
1.0
1.5
2.0
1.0
1.5
2.0
1.5
2.0
0.5
1.0
1.5
Example :-
Then :-
System Volume = 75 litres
Vessel Charge Pressure = 1.0 bar
Initial System Pressure = 1.5 bar
75 x 0.152 = 11.4 litres
Expansion Vessel Volume
Method of determining minimum
value of expansion vessel volume for
sealed systems using Baxi Boilers
NOTE
Where a vessel of the calculated size is not obtainable
then the next available larger size should be used.
Safety
Valve
Pressure
Gauge
Pump
Filling
Point
Air
Vent
3 Litre
Top Up Bottle
(if required)
Radiator
Circuit
Expansion
Vessel
System Drains at
Low Point
Max Boiler Flow
Temp = 82° C
Boiler
Fig. 9
Table. 1
Stop
Valve
Double
Check
Valve
DHW
Mains
Inlet
CH
Return
Temporary
Hose
Stop
Valve
Fig. 9a
