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WD53/0/1999
Chapter 1 : General Instruction
1.1
DESCRIPTION
The Keston 260 and 340 Condensing Boilers are unique in their concept and design. They
comprise two boiler modules with individual gas valve, fans, burners and heat exchanger
assemblies. The two modules are fully independent in operation and are automatically
sequenced to provide optimum load matching. In addition, firing sequence is regularly
rotated to ensure even usage levels. While the application for which the boilers were
designed is the same as those which other boilers are used, the Keston boiler has the
added advantage of very high efficiency, and small diameter plastic flue which can be
extended to 20 metres horizontally or vertically. The Keston 260 and Keston 340 are
designed to be wall hung. However, floor standing installation can be accommodated by
using the optional floor standing frame.
The Keston module uses a high power combustion blower to deliver a pre-mix of gas and
air to a downward firing burner in a high efficiency, single pass heat exchanger. The flue
system is room sealed and fan powered. The ignition is direct spark and fully automatic.
The boiler housing is not waterproof and should be installed in a position where it will
always be dry. Consideration should also be given to the noise levels generated by the
combustion fan when in operation. Small air intake points are incorporated within the
appliance cabinet to ensure that the interior of the cabinet is maintained under a slight
negative pressure. This is a safety feature to reduce the possibility of products leakage
out of the cabinet into the installation space..
The boiler is suitable for connection to open vented or, preferably, sealed systems. The
system must be pumped central heating or pumped central heating with combined indirect
sanitary hot water. Gravity circuits must not be used.
Forming part of each boiler module is the heat exchanger which is made from a highly
corrosion resistant stainless steel, formed into tightly wound coil. The hot combustion
gases from the central down firing burner pass through this coil imparting heat into the
system water. Integral module shunt pumps within the appliance cabinet ensure each
module receives correct water flow when firing. The Keston boiler is not a high water
content boiler and does not contain the metal mass, or water volume, of a cast iron or
steel boiler. This boiler is of low mass and low water content and therefore responds
faster when there is a call for heat.
1.2
BOILER SCHEMATIC
Air is drawn into the boiler through a 100mm composite plastic pipe. Each module air flow
is proved by a differential pressure across the air control orifice. Gas is mixed with
combustion air at the inlet to the fan. The gas flow is regulated by an orifice located in the
housing downstream of the gas valve. The gas and air are thoroughly mixed in the blower
and fed into the burner located at the top end of the heat exchanger module. The gas and
air mixture is ignited by a direct spark ignition control system and burns with a blue flame
just off the surface of the burner. As the hot products of combustion pass downwards,
they are cooled by exchanging heat with the circulating water which enters the heat
exchanger coil at the bottom of the heat exchanger.
When the return water temperature is below 55
combustion products will condense inside the heat exchanger, thus increasing the boiler
efficiency further by releasing the latent heat of condensation. This condensate falls to the
bottom of the heat exchanger where it is separated from the flue gases and exits from the
boiler through the condensate drain. Any condensate formed in the flue runs back down
the flueway and is drained at the base of the flue connection to the heat exchanger or
drain points within the flue.
Installation & Servicing Instructions
1. GENERAL INSTRUCTION
The Keston 260 & 340 Condensing Boilers
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C, part of the water vapour in the
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