General Instruction; Description; Boiler Schematic - Keston Celsius 25 Installation And Servicing Instructions

WD209/1/2000 Chapter 1 : General Instruction
1.1

DESCRIPTION

The Celsius 25 is unique in its concept and design. It comprises a high efficiency stainless
steel heat exchanger coupled with a low emissions burner to deliver ultra high efficiency
condensing mode operation within a compact wall hung cabinet. The unit automatically
adjusts gas and air rate according to demand to give an output in the range of 7.0kW to
25.2kW (natural gas model). The integral standard UPS Grundfos pump is automatically
controlled across the three speeds to best match water flow rate to heat output & further
increase appliance efficiency. While the application for which the Celsius 25 was designed
is the same as those which other boilers are used, the Keston Celsius 25 has the added
advantage of very high efficiency, and small diameter plastic flue which can be extended
up to 60 metres horizontally or vertically.
The Keston Celsius 25 uses a variable speed combustion blower to deliver a premix 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. Combustion air is drawn from the cabinet which is connected
to outside atmosphere via a small diameter plastic intake pipe. The cabinet therefore
remains under negative pressure at all times the boiler is operating.
The boiler is suitable for connection to open vented or, preferably, sealed systems.
The boiler heat exchanger is made from highly corrosion resistant stainless steel in
corrugated pipe form which provides massive surface area within a compact dimension.
The hot combustion gases from the down firing burner pass around the stainless steel
pipes imparting heat into the system water. The integral standard 3 speed Grundfos pump
within the appliance cabinet ensures the heat exchanger receives correct water flow when
firing. The Celsius 25 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. The Celsius 25
features full user diagnostics, integral frost protection thermostat, automatic pump and fan
exercise in periods of inactivity, anti cycle control, dry fire protection and connections for
remote lockout and run monitoring.
1.2

BOILER SCHEMATIC

Air is drawn into the boiler through a 50 mm muPVC (BS5255 and/or BSEN1566-1 and
BSEN1329) plastic pipe or, alternatively, via a 75mm composite plastic pipe.. Gas is
mixed with combustion air at the inlet to the fan. The gas flow is automatically regulated by
the gas valve according to the air flow generated by the fan. 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 at the bottom of the heat exchanger. The optimum
heat input is detected by monitoring flow and return temperatures and is adjusted by
controlling the speed of the fan. The optimum pump speed is also detected and
automatically selected by the boiler.
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 Celsius 25 & 25P
O
C, part of the water vapour in the
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