Technical data

© Baxi Heating UK Ltd 2010
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3.10 Water Circulating Systems
The boiler is suitable for use with fully pumped open
vented and sealed systems with an indirect coil type high
efficiency cylinder.
The following conditions should be observed on all
systems:
• The static head must not exceed 30.5 m (100ft)
(3 bar) of water or be less than 150 mm (6 in).
• The flow pipe from the boiler must always be higher
than the return pipe.
• To ensure correct operation, the pump must be wired
to the boiler terminal block.
3.10.1 Treatment of Water Circulating Systems
1. All recirculatory water systems will be subject to
corrosion unless they are flushed and an appropriate
water treatment is applied. To prevent this, follow the
guidelines given in BS 7593 “Treatment of Water in
Domestic Hot Water Central Heating Systems” and the
treatment manufacturers instructions.
2. Treatment must involve the use of a proprietary
cleanser, such as Sentinel X300 or X400, or Fernox F3
and an inhibitor such as Sentinel X100 or Fernox MB-1.
3. Full instructions are supplied with the products, for
further information contact Sentinel (0800 389 4670) or
Fernox (0870 870 0362).
Failure to flush and add inhibitor to the system will
invalidate the appliance warranty.
4. It is important to check the inhibitor concentration
after installation, system modification and at every
service in accordance with the inhibitor manufacturer’s
instructions. (Test kits are available from inhibitor
stockists.)
5. For information or advice regarding any of the above
contact Technical Enquiries 0844 871 1555.
3.10.2 System Design
Pipe Sizing
The flow and return connections on the boiler are 22
mm. The sizes of the system flow and return pipes from
the boiler should be determined by normal methods,
according to the system design requirements. See Fig.
30. and Table 2.
Air Vents
It is recommended that automatic air vents are fitted
within the system pipework to prevent air locks during
filling, commissioning and normal operation.
To ensure correct circulation, it is essential to vent all air
from the system prior to commissioning the boiler.
System Drain Off Points
Drain off points should be fitted in the pipework close to
the boiler and in the low points of the system.
Plastic Pipework
If plastic pipe is used for the central heating circuit there
must be a run of at least 2 metres of uninsulated copper
pipe from the boiler flow and return connections
including any branches.
3.10.3 Bypass Requirements
The system must be designed to always provide a route
for water to circulate between the boiler flow and return.
Best Practice is to use an automatic bypass although it
may be possible to use an existing fixed bypass such as
a landing or bathroom radiator fitted with two lockshield
valves or a bypass fitted with a balancing valve. See
Fig. 30.
Systems with Two Port Valves
Where a pair of two port zone valves are used, the total
length of the by-pass circuit taken from the boiler
connections should be greater than 4 metres of 22 mm
pipe. The bypass should be capable of maintaining a
minimum flow through the boiler of 4.5 litres/min (1
gal/min).
Systems with Thermostatic Radiator Valves (TRV’s)
Where mechanically operated thermostatic control
valves are used, the total length of the by-pass circuit
taken from the boiler connections should be greater
than 2 metres of 22 mm pipe. The bypass should be
capable of maintaining a minimum flow through the
boiler of 9.0 litres/min (2 gal/min).
3.10.4 System Controls
For optimum operating efficiency, the heating system
into which the boiler is installed should include a control
system. Best Practice suggests such a system should
comprise: a programmer, room and cylinder
thermostats, control valves giving boiler interlock.
Frost Protection - System
The system pipework may require insulation and the
protection of an additional frost thermostat.
If the system is drained isolate the external gas and
electrical supplies.