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WATER CIRCULATION SYSTEM
A circulation pump MUST be connected to the boiler, see
below.
The boiler must NOT be used for direct hot water supply.
The hot water storage cylinder MUST be of the indirect type.
Single feed, indirect cylinders are not recommended and
MUST NOT be used on sealed systems.
The appliances are NOT suitable for gravity central heating
nor are they suitable for the provision of gravity domestic hot
water.
The hot water cylinder and ancillary pipework, not forming
part of the useful heating surface, should be lagged to
prevent heat loss and any possible freezing - particularly
where pipes run through roof spaces and ventilated un-
derfloor spaces.
The boiler must be vented. There must be no low points
between the boiler flow connection and a system vent point,
which should be positioned as close as practically possible
to the boiler flow connection.
Draining taps MUST be located in accessible positions,
which permit the draining of the whole system - including
the boiler and hot water storage vessel. They should be at
least 1/2" BSP nominal size and be in accordance with
BS. 2879. Do not use the boiler drain tap to drain the
system as this can induce sludge into the heat exchanger.
The central heating system should be in accordance with
the relevant standards listed on page 8.
Due to the compact nature of the boiler the heat stored
within the castings at the point of shutdown of the burner
must be dissipated into the water circuit in order to avoid
overheating. In order to allow pump operation after burner
shutdown the boiler control incorporates a pump overrun
facility. In order to make use of this, a pump must be sup-
plied from the terminals inside the boiler.
requiring greater than 1.0 amp current, they must be con-
nected via a relay.
When sizing pumps, reference should be made to the
Hydraulic Resistance
Table on page 12
boiler resistance against flow rates, to achieve the required
temperature differential.
Flow rates for common systems using either 11
temperature differentials are given in the table below.
Note.
With the boiler firing at maximum rate, the temperature
differential should not be less than 10°C. Higher flow rates
required for lower temperature differentials could lead to
erosion of the heat exchanger water ways.
With the boiler firing at minimum rate, the temperature differ-
ential should not be greater than 26°C. Lower flow rates gen-
erating higher temperature differentials will lead to lock out of
the boiler.
The lower the return temperature to the boiler, the higher the
efficiency. At return temperatures of 55°C and below, the dif-
ference becomes marked because the water in the flue gases
starts to condense, releasing its latent heat.
In installations where all radiators have been provided with
thermostatic radiator valves, it is essential that water circula-
tion through the boiler is guaranteed. A mixing header will per-
form this task. Alternatively this can be best achieved by
means of a differential pressure valve, which is installed in a
bypass between the flow and return pipes. The bypass should
be fitted at least 6m from the boiler, and should be capable of
allowing a minimum flow rate to achieve a temperature differ-
ential of no greater than 26°C at minimum rate.
Note: for pumps
which show the
o
o
C or 20
C
flow rate
Water
temp. difference
11°C
Boiler
l/s
m
3
303
1.4
5
304
1.9
7
305
2.5
9
3.1
11
306
307
3.6
13
flow rate
Water
temp. difference
20
o
C
/h
l/s
m
/h
3
0.8
2.9
1.1
4.1
1.4
5.2
1.8
6.6
2.3
8.2
11
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