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WD51/0/1997
4.6
HOT FLUSHING
a.
Allow the system to heat up, checking for water soundness.
b.
Follow instructions provided with the cleaning agent, ie Fernox Supafloc. Turn off
the boiler and flush the water system while still hot. Thoroughly flush the system
with clear water.
c.
Refill the system using a quality water treatment such as Fernox CP3. For sealed
systems, fill to the required Initial Design Pressure.
4.7
CHECKING THE GAS PRESSURE
With the boiler running measure the
burner pressure at the burner pressure
test nipple.
The gas setting is factory adjusted to
within the required range and should not
normally need re-adjustment unless the
unit has also been converted to LPG as
part of the installation. If the reading is
incorrect then check such factors as
soundness of the air and flue pipe joints
and the gas inlet pressure (20 mbar
required). If all joints are sound and the
gas inlet pressure is satisfactory remove
the brass dust cap covering the burner
pressure adjustment screw on the gas
valve (See fig. 4.7). Set the gas pressure to the required value as stated in table 4.7 by
turning the exposed burner pressure adjustment screw (clockwise will increase burner
pressure, anti-clockwise will decrease burner pressure).. This will ensure that combustion
is good enough to allow combustion fine tuning to take place. Replace the brass dust cap
to cover the burner pressure adjustment screw.
4.8
TIMING THE GAS METER - NATURAL GAS
After the boiler has been started, and with no other appliances using gas, time the gas
meter to be certain that the unit is running at the proper gas input. Determine the cubic
feet of gas passing through the meter and determine the input in Btu per hour. Input must
be within plus or minus 3% of the rated input.
Time, in seconds, the time taken to pass 2 cubic feet of gas through the meter (ie one
revolution of a 2 cu ft dial) or 0.1 cubic metres if the meter is of the new metric digital type.
The Keston 170, when correctly set, should take 39.8 seconds for 2 cubic feet of natural
gas and 70.3 seconds for 0.1 cubic metres of natural gas (assuming 1038 btu/h per cubic
foot). Adjust the gas valve screw clockwise to increase the input (speed up the meter) or
anticlockwise to decrease the input (slow down the meter) accordingly.
4.9
COMBUSTION FINE TUNING
Although the gas pressure is preset at the factory differing flue arrangements may require
fine tuning of the gas pressures to produce the best combustion and ensure long burner
life. It is advisable to check proper combustion by measuring gas input and the level of
carbon dioxide, or oxygen, in the flue outlet from the boiler. Overfiring or underfiring the
burner will reduce the longevity of the appliance.
Installation & Servicing Instructions
Chapter 4 : Commissioning
Burner pressure
Adjustment
Burner pressure
test nipple.
The Keston 170 Condensing Boiler
Fig 4.7
GAS VALVE
Page : 23
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