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Publication No. 560100 Installation Requirements 11
Installation Requirements - Page 11
1.6 The System
The boiler must be used on INDIRECT hot water systems only.
It is suitable for use on open vented gravity domestic hot
water/pumped central heating systems or, fully pumped
systems which may be sealed or open vented.
Existing systems should be thoroughly cleansed prior to boiler
installation.
The system should be designed so that the maximum static
head does not exceed 30.5m and a minimum on fully pumped
systems of 300mm. See Fig. 8.
Gravity domestic hot water circuits should have a minimum
circulating head of 1.2m. See Fig. 7. Horizontal pipe runs
should be kept to a minimum.
To prevent reverse circulation in the gravity circuit when the
pump is running an injector tee is incorporated.
The pump should preferably be fitted in the flow, though
installation in the return is acceptable providing care is taken to
ensure air is not drawn into the system due to the negative
pressure effects of the pump. Isolating valves must be fitted as
close as possible to allow replacement without system
draining.
Drain off taps should be fitted in the pipework close to the
boiler and in the low points of the system. A drain point is also
provided on the heat exchanger should the boiler need
draining - see Fig. 17.
Combined Gravity Hot Water Pumped
Central Heating Systems.
Where a cylinder thermostat and zone valve are used to
control the temperature of the 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. 7. where the bathroom
radiator is connected into the gravity circuit and is fitted with
two lockshield valves. Mechanically operated thermostatic
domestic hot water temperature control valves which allow the
boiler to operate when the valve is closed or partially closed
MUST NOT BE FITTED unless a bypass radiator is fitted.
Note: The boiler has one flow and two return connections. On
combined gravity DHW/Pumped central heating a Tee will be
needed in the flow which must be fitted directly to the
connecting pipe provided.
Fully Pumped Systems
The pump must be wired directly to the terminal block
(See Fig. 15) as it will allow the pump to be controlled by the
over-run device. This will ensure that the pump will continue to
run after boiler shut down thus preventing nuisance operation
of the overheat thermostat.
If a three port diverter valve is used as shown in Figs.8 & 9, 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. It should be fitted with a lockshield valve and be
adjusted to maintain a minimum flow through the boiler of 4.5
litres/min (1 gal/min) see Figs. 8 & 9.
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 1kW (3,400 Btu/h)
2. Maintaining a minimum water flow through the boiler
of 9 litres/min (2 gal/min).
A suggested method of meeting these requirements by using
a bathroom radiator fitted with two lockshield valves is shown
in Figs. 8 & 9.
Diagrammatic layouts of a fully pumped system and a
combined pumped central heating/gravity hot water system
are shown in Figs. 7 & 8.
Sealed Systems (Fully Pumped)
Installation
The installation must comply with the requirements of BS
6798: 1987 and BS 5449: Pt 1. The British Gas publication
"British Gas Specification for Domestic Wet Central Heating
Systems" should also be consulted.
Safety Valve
A non-adjustable spring-loaded safety valve, preset to operate
at 3 bar (45lbf/in²) shall be used. It must comply with BS 6759:
Pt 1. and include a manual testing device. It shall be
positioned in the flow pipe either horizontally or vertically
upwards and close to the boiler. No shut-off valves are to be
placed between the boiler and the safety valve. The valve
should be installed into a discharge pipe which permits the
safe discharge of steam and hot water such that no hazard to
persons or damage to electrical components is caused.
Pressure Gauge
A pressure gauge incorporating a fill pressure indicator,
covering the range 0 - 4 bar (60 lbf/in²) shall be fitted to the
system. It should be connected to the system, preferably at
the same point as the expansion vessel. Its location should be
visible from the filling point.
Expansion Vessel
A diaphragm type expansion vessel to BS 4814: Pt 1. shall be
fitted close to the inlet side of the pump. The connecting
pipework should not be less than 15mm. Pipework connecting
the expansion vessel should not incorporate valves of any
sort. Methods of supporting the vessel are supplied by the
vessel manufacturer. The nitrogen or air charge pressure of
the expansion vessel shall not be less than the hydrostatic
head, (height of the top point of the system above the
expansion vessel).