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TECHNICAL DATA - Page 8
THE SYSTEM
The boiler must be used on INDIRECT hot water systems
only. It is suitable for use on open vented gravity hot
water/pumped central heating systems or fully pumped
systems which may be sealed or open vented.
The system should be designed so that the maximum static
head does not exceed 30.5m (l00ft) and a minimum on fully
pumped systems of 150mm (6in). See Fig 5. Gravity
domestic hot water circuits should have a minimum
circulating head of 1.2m (4ft). See Fig 6. Excessive
horizontal runs should be avoided, but if this not possible
the circulating head should be increased.
If the boiler is to be used on a system with gravity hot water
the bulb of the overheat thermostat should be repositioned
as shown on Figs 2 & 18.
To prevent reverse circulation in the gravity circuit when the
pump is running an injector disc is provided to form an
injector tee at the return connection on the boiler.
See Fig 17.
To prevent nuisance operation of the overheat thermostat,
it is important that where electrically operated zone valves
are used the boiler is wired so that it does not cycle when
the zone valves are closed. Also systems fitted with
controls that close both hot water and central heating
circuits while the boiler is still hot must be fitted with a by-
pass circuit to dissipate the residual heat within the boiler.
Further information on by-pass arrangements is provided in
later notes and illustrations.
Drain-off taps should be fitted in the pipework close to the
boiler and in low points in the system.
NOTE
Although the system can be emptied using the drain-off
taps in the pipework around the system, to empty the boiler
it is necessary to remove the drain-off plug situated in the
return header at the lower right-hand side of the casting.
See Fig 2.
COMBINED GRAVITY HOT WATER AND
PUMPED CENTRAL HEATING SYSTEMS
Where a cylinder thermostat and zone valve are fitted to
control the temperature of the domestic hot water it is
recommended that a by-pass be installed in the gravity
circuit. A suggested method of doing this is shown in Fig 6
where the bathroom radiator is connected into the gravity
circuit and is fitted with two Iockshield valves. Mechanically
operated thermostatic domestic hot water temperature
control valves which allow the boiler to operate when the
valve is closed
MUST NOT BE FITTED.
FULLY PUMPED SYSTEMS
The pump must always be wired directly to the
boilerterminal block as shown in Fig 21. If a three port
diverter valve is used as shown in Fig 5 a by-pass is not
necessary since one circuit is always open.
Where a pair of two port valves are used, a by-pass is
necessary. The total length of the by-pass circuit taken
from the boiler connections should be greater than 4
metres of 22mm pipe. It should be fitted with a lockshield
valve and adjusted to maintain a minimum flow through the
boiler of 4.5 litres/mm (1 gal/mm), see Figs 5 &7.
Systems fitted with controls which allow the boiler to
operate when both the hot water and central heating
circuits are closed (i.e. mechanically operated thermostatic
control valves) must be fitted with a by-pass circuit capable
of:-
1.
Dissipating a minimum of 1 kW (3400 Btu/h).
2.
Maintaining a minimum water flow through the boiler of
9 litres/mm (2 gal/mm).
A suggested method of meeting these requirements by
using a bathroom radiator fitted with two lockshield valves
is shown in Figs 5 & 7.
Additional system information can be found in the Control
Systems, Pipework and wiring guide.
SEALED SYSTEMS (FULLY PUMPED)
The installation must comply with the
requirements of BS6798 and BS5449 Part 1.
The British Gas publication ‘British Gas
