When thermostatic radiator valves are fitted, the system must
incorporate an adequate automatic by-pass.
Fig. 12 - Sealed System
Sealed central heating system
\
5.11
22
Outdoor Combi 90 V3, Combi Max and Condensing Combi
5 - GENERAL BOILER INFORMATION
See Fig. 16
1 The boilers are only suitable for use with a sealed system
complying with the requirements of BS 5449. The
maximum temperature of the central heating water is 85˚C
for the Combi 90 V3 and Combi Max and 75˚C for the
Condensing Combi models.
Design notes -
when designing the system, the pump head,
expansion vessel size, radiator mean temperature, etc. must
all be taken into account.
2 The boilers are supplied with the following items factory
fitted:
a 12 litre diaphragm expansion vessel complying with BS
4814, pre-charged at 1.0 bar. A 14 litre vessel is fitted in
the Condensing Combi 36 model.
b System pressure gauge, with an operating range of 1 to
4 bar.
c Pressure relief safety valve complying with BS 6759 and
set to operate at 2.5 bar. The discharge pipe must be
routed clear of the boiler to a drain, in such a manner
that it can be seen, but cannot cause injury to persons or
property.
d Automatic air vent, fitted to the top of the boiler, ensures
the boiler is vented.
e Filling loop. This
must be
isolated and disconnected
after filling the system.
3 Refer to Sections 4.1 or 4.2 for maximum heating system
volume and BS 7074: for further guidance. If the system
volume
exceeds
the maximum value given for the boiler, an
additional vessel will be required. This should be connected
to the system on the return. Refer to Fig. 12.
Refer to Section 6.5 for further details of the expansion
vessel.
4 The system design pressure (cold) should be between 0.5
and 1.0 bar. This pressure is equivalent to the maximum
static head (see Fig. 16) in bar + 0.3 (1 bar = 10.2 metres of
water).
5 When thermostatic radiator valves are fitted, a system by-
pass must be fitted. The by-pass must be an automatic type.
6 Provision should be made to replace water lost from the
system. This may be done manually (where allowed by the
local Water Undertaking) using the filling loop arrangement
supplied with the boiler.
7 Filling of the system must be carried out in a manner
approved by the local Water Undertaking. Where allowed,
the system may be filled via the filling loop supplied (the
loop arrangement includes a double check valve assembly).
8 All fittings used in the system must be able to withstand
pressures up to 3 bar.
9 Radiator valves must comply with the requirements of BS
2767(10):1972.
10 One or more drain taps (to BS 2879) must be used to allow
the system to be completely drained.
11 The expansion vessel is connected via a flexible hose to
allow it to be moved to gain access to the cleaning cover.
When replacing the vessel, care should be taken to ensure
that the flexible connecting hose is not twisted.
