12
0020003579A
Diagram 2.2
FULLY PUMPED SYSTEM
(DIAGRAMMATIC)
2 Water Systems
0870
The working pressure must be within the range 0.1bar to 2.7bar
(1.3 to 39lbftin
2
).
The boiler MUST NOT be connected to a sealed water system.
2.2 Inhibitor
Attention is drawn to the current issue of BS5449 and BS7593
on the use of inhibitors in central heating systems.
If an inhibitor is to be used in the system, contact should be
made with the inhibitor manufacturers so that they can
recommend their most suitable product.
When using in an existing system take special care to drain the
entire system, including the radiators, then thoroughly clean out
before fitting the boiler whether or not adding an inhibitor.
2.3 Gravity Domestic and Pumped Heating
It is recommended that a cylinder thermostat is used to prevent
the stored water temperature becoming unnecessarily high
when the central heating pump is off.
The domestic primary flow and return must be 28mm o.d. The
installation must comply with the current issue of BS5546 and
BS6700, see diagram 2.1.
If the above conditions cannot be met, it is suggested that a fully
pumped system be used.
2.4 Pumped Heating and Hot Water
Where a single flow and return is taken from the boiler, a
minimum static head of 1 metre (3ft3in) must be provided
between the water line of the feed tank and the centre of the
waterway, see diagram 2.2.
2.5 Circulation Pump
Normally the pump should be set to give a temperature difference
of 11
o
C (20
o
F) across the boiler. At the appropriate pumped flow
rate the pressure loss through the boiler can be found from the
graph, diagram 2.3.
Use a pump with integral valves or fit isolating valves as close
to the pump as possible.
2.6. Cylinder
For all systems supplying domestic hot water the cylinder must
be indirect.
2.7 Safety Valve
A safety valve need not be fitted to an open vented system.
2.8 Draining Tap
A draining tap must be provided at the lowest points of the
system which will allow the draining of the entire system,
including the boiler and hot water cylinder.
Draining taps should be to the current issue of BS2879.
2.9 Thermostatic Radiator Valves
If thermostatic radiator valves are fitted care must be taken to
ensure that there is an adequate flow rate through the boiler
when they close, refer to the current issue of BS7478 for
guidance. If fitted to all radiators ensure a bypass is fitted and
adjust to achieve a temperature difference no greater than 20
o
C
between flow and return with the thermostatic valves closed.
Diagram 2.3
1370
1.0
0.8
0.6
0.4
0.2
0
30
20
10
0
0
10
20
30
40
50
FLOW RATE (LITRES/MINUTE)
WATER PRESSURE LOSS
(metre HEAD OF WATER)
WATER PRESSURE LOSS
(INCHES HEAD OF WATER)
1.2
40
0 1 2 3 4 5 6 7 8
10
9
FLOW RATE (GALLON/MINUTE)