Grant Combi 26e User Manual

19
7.1 System Models
All Grant Vortex Pro External Combi
e boilers are supplied as part of a
sealed system that complies with the
requirements of BS 5449.
The maximum temperature of the
central heating water is 78° C.
When designing a system, the
pump head, expansion vessel size,
and radiator mean temperature are
amongst the factors that must be
considered. See Section 4.6.
The boilers are supplied with the
following items factory fitted*:
• A 24 litre diaphragm expansion
vessel complying with BS 4814,
pre-charged at 1.0 bar.
• 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. 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.
• Automaticairvent,ttedtothetop
of the boiler, ensures the boiler is
vented.
• Fillingloop.Thismustbeisolated
and disconnected after filling the
system.
Refer to Section 4.5 for further details
of the expansion vessel.
The expansion vessel charge pressure
should always be slightly greater than
the maximum static head of the system,
in bar, at the level of the vessel (1 bar =
10.2 metres of water). See Figure 7-1.
The system fill pressure (cold) should
be 0.2-0.3 bar greater than the vessel
charge pressure - giving typical system
fill pressures of approx 0.5 bar for a
bungalow and 1.0 bar for a two-storey
house. Refer to the Domestic Heating
Design Guide for more information if
required.
If thermostatic radiator valves are fitted
to all radiators, a system by-pass
must be fitted. The bypass must be an
automatic type.
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.
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).
All fittings used in the system must be
able to withstand pressures up to 3
bar.
Radiator valves must comply with the
requirements of BS 2767(10):1972.
One or more drain taps (to BS 2879)
must be used to allow the system to be
completely drained.
The expansion vessel is connected via
a flexible hose to allow it to be moved
to gain access to the baffle cleaning
cover. When replacing the vessel, care
should be taken to ensure that the
flexible connecting hose is not twisted.
7 Sealed Systems
Figure 7-1: Sealed system
Static head of system
Heating flow
Heating
return
By-pass if required
(automatic type)
350mm
Boiler
Expansion
vessel
If thermostatic radiator valves
are fitted, the system must
incorporate an adequate
automatic by-pass.
Stop valve
Water mains
Domestic
hot water
Domestic
cold water
!
NOTE
Ensure that the expansion vessel
is of sufficient size for the system
volume (including the volume of
the boiler). If necessary a second
vessel may need to be fitted to
the system. Refer to Section 2.1
for system volume. To determine
total vessel volume required refer
to BS7074:1:1989 or the Domestic
Heating Design Guide.
!
NOTE

Grant Combi 26e Specifications

General

Boiler Type	Combi
Output	26 kW
Fuel Type	Natural Gas
Efficiency	90%
Mounting	Wall-mounted