3.7.3
Boiler By-pass Piping
Boiler water flows are critical to the operation of the boiler. If flow cannot be
maintained through the system piping to meet the minimums required by the
boiler, insufficient water flows through the boiler will cause the boiler to "kettle" or
even produce steam which can damage the heat exchanger and will invalidate the
heat exchanger warranty. In addition, an open circuit is required after boiler
shutdown to permit circulation during the boilers 2 minute pump overrun
sequence.
It is advisable to incorporate a boiler by-pass in the system, especially if
thermostatic radiator valves are used. The flow/return differential should be 10
o
C
to 20
o
C. To comply with the Building Regulations Part L1 the bypass must
of the automatic type.
3.7.4
Hot Water System (if applicable)
The hot water storage vessel must be of the indirect type (certain direct cylinders
can be used provided they are suitably adapted by fitting an immersion calorifier).
DIRECT CYLINDERS MUST NOT BE USED. Further guidance is provided in BS
1394. It is advisable to fit a locksheild valve on the cylinder return to enable
balancing of the flow rate through the cylinder.
The Keston qSpa range of stainless steel unvented cylinders are an ideal
option for use with the Keston range. The Keston qSpa range combine
exceptional recovery times with durable, long life stainless steel
construction and all associated controls. Contact Keston Boilers Ltd for
information.
The Keston Q37 also has advance control options built in which enable
modulated reheat of DHW. Refer to Chapter 4 for more detail.
3.7.5
Air Elimination
In the initial charge of water to the boiler system and in all subsequent additions
of water to the system some air will be dissolved in the water. As the water is
heated the air is driven out of the solution and will collect in high spots in the
system. These air bubbles can interfere with pumping and heat transfer and
must be eliminated.
Installation of air bleed valves at the high spot(s) in the system will allow for air
elimination when filling the system and will allow re-venting in a day or so after all
air has been driven out of solution.
3.7.6
System Pump Selection (if required)
The Keston Q37 features an integral circulating pump which has sufficient excess
head to drive most domestic systems. The available head is shown in the graph
below (Diagram 3.7.6). If the system index circuit resistance is in excess of the
available head from the integral pump an additional system pump will be required.
The schematic below illustrates a recommended approach to using an additional
system pump (Figure 3.7.6). The additional system pump should be sized to
overcome the index circuit resistance only as the boilers integral pump will
overcome boiler resistance.
If an additional pump is required the selected pump must comply with BS 1394.
Provision must be made in the system design for control of the additional pump. A
connection point is available within the boiler to signal operation of the additional
pump. However, this will need to drive the additional pump via a suitable relay.
WD500
Chapter 3 - Boiler Location
The Keston Q37 & Q37P Boilers
Installation & Servicing Instructions
Page : 16
