Installation Manual

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. On the Qudos 28s integral variable speed
pump within the appliance cabinet ensures the heat exchanger receives correct water flow
when firing. The Qudos 28s 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 Qudos
28 features full user diagnostics, integral frost protection function, automatic pump and
fan exercise in periods of inactivity, anti cycle control and dry fire protection.
2.2 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 Keston 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
o
C, part of the water vapour in the
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
WD420/3/2007 Chapter 2 : General Instruction The Keston Qudos 28s & Qudos 28sP Boilers
Installation & Servicing Instructions Page : 5
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