8
221462C
Notes:
PUMP
The pump with integral valves, if possible, should be fitted in the
flow pipework from the boiler, to produce a temperature difference
across the boiler of 11
o
C (20
o
F).
See diagram 3.1 for pressure loss across the boiler.
High resistance microbore systems may require a higher duty
pump.
BYPASS
A bypass must be fitted, see diagram 3.2.
The flow through the boiler must not be allowed to fall below:
50C - 13.2L/min (2.9gall/min)
whilst the burner is alight.
3.1 Open (Vented) Water System
For an open (vented) water system the boiler must be supplied
from an unrestricted water supply taken from a cold feed and
expansion cistern situated at a maximum height of 27.5 metres
(90ft) above the boiler.
The cold feed supply must be 15mm minimum size.
It is important that the relative position of the pump, cold feed
and open vent are as shown in diagram 3.2.
3.2 Domestic Hot Water Cylinder
The domestic hot water cylinder must be of the double feed, fully
indirect type. Single feed, self priming cylinders are not
recommended.
3.3 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, contact a manufacturer for their
recommendations for the best product to use.
When installing a boiler in an existing system, whether or not
using an inhibitor, take special care to drain the entire system,
including the radiators, then thoroughly cleaning out before
fitting the boiler and adding the inhibitor.
3.4 Sealed Water Systems
The installation should comply with the appropriate requirements
of the current issue of BS4814, BS5449, BS6759, BS6798 and
BS7074 Part 1 and 2.
See diagram 3.3 for a diagrammatic layout.
3.5 Safety Valve
A safety valve must be fitted to a sealed water system.
It shall be preset, nonadjustable with a lift pressure of 3bar,
incorporating seating of a resilient material, a test device and a
connection for drain.
The drain from the safety valve must be routed clear of any
electrical fittings and positioned so that any discharge can be
seen.
Diagram 3.1
PRESSURE LOSS OF BOILER
Diagram 3.2
Open (vented) system.
Recommended
relationship between
pump, cold feed and
vent.
22 mm (MIN) VENT
FEED AND
EXPANSION
CISTERN
15mm (MINIMUM)
COLD FEED
15mm (MINIMUM)
BY-PASS WITH
LOCKSHIELD VALVE
450mm
MIN.
HEIGHT
1150mm
MIN.
150
mm
MIN.
BOILER
PUMP
150mm
MAX
FLOW
RET.
ALTERNATIVE
PREFERRED
RET.
CYLINDER
FLOW
HEATING
0392
3 Water Systems
GALLONS/MINUTE
LITRES/MINUTE
FUELSAVER 50C
WATER PRESSURE LOSS
(m head of water)
WATER PRESSURE LOSS
(in head of water)
0
1
2
4
3
5
0
5
10
15
20
25
55
50
45
40
35
30
25
20
15
10
5
0
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0
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