22
The air pressure in the vessel must be
checked annually.
The central heating system volume,
using the expansion vessel as supplied,
must not exceed the recommended
value. Refer to Section 2.2. If the system
volume is greater, an extra expansion
vessel (complying with BS 4841) must be
fitted as close as possible to the central
heating return connection on the boiler.
The charge pressure of the extra vessel
must be the same as the vessel fitted in
the boiler.
Refer to either BS 7074:1:1989 or The
Domestic Heating Design Guide for
the required total expansion vessel
volume for the system concerned.
The air charge pressure may be checked
using a tyre pressure gauge on the
expansion vessel Schraeder valve. The
vessel may be re-pressurised using a
suitable pump. When checking the air
pressure the water in the heating system
must be cold and the system pressure
reduced to zero.
Sealed Systems
7.2 System Models
All System models have the following
sealed system components factory fitted
(refer to Figure 7-3):-
• A diaphragm expansion vessel
complying with BS 4814, pre-charged
at 1.0 bar. Refer to Section 2.2.
• System pressure gauge, with an
operating range of 1 to 4 bar.
• Pressure relief safety valve complying
with BS 6759 and set to operate at
2.5 bar.
• Automatic air vent, fitted to the flow
pipe of the boiler, ensures the boiler
is vented.
• Filling loop. This must be isolated and
disconnected after filling the system.
Refer to Section 2.2 for system volumes
and BS 7074: for further guidance and
for further details of the expansion
vessel.
The expansion vessel fitted, is supplied
with a charge pressure of 1.0 bar
(equivalent to a maximum static head of
10.2 metres). The charge pressure must
not be less than the actual static head at
the point of connection.
Do not pressurise the vessel above
1.5 bar.
Figure 7-3: Sealed system components
CAUTION
!
7.3 Fill the Sealed System
Automatic air vent(s) are fitted to the top
of the boiler (see Figure 7-3). Check that
the small cap on the top of each air vent
is screwed on fully, then unscrew it one
complete turn - the cap remains in this
position from now on.
The procedure for filling the sealed
system is as follows:
1. Only ever fill or add water to the
system when it is cold and the boiler
is off. Do not overfill.
2. Ensure that the flexible filling loop
supplied with the boiler is connected
and that the double check shut off
valve connecting it to the water supply
is closed.
A valve is open when the operating
lever is in line with the valve, and closed
when it is at right angles to it.
3. Open the fill point valve.
4. Gradually open the double check valve
from the water supply until water is
heard to flow.
5. When the white needle of the pressure
gauge is between 0.5 and 1.0 bar, close
the valve.
6. Vent each radiator in turn, starting
with the lowest one in the system, to
remove air.
NOTE
!
NOTE
!
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