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6.6
SETTING THE AIR/GAS RATIO
NOTICE: THE SETTING OF THE GAS RATIO
MUST BE CARRIED OUT BY A COMPETENT
PERSON. SETTING OF THE GAS RATIO
MUST NOT BE ATTEMPTED UNLESS THE
PERSON CARRYING OUT THE TEST IS
EQUIPPED WITH A COMBUSTION
ANALYSER CONFORMING TO BS 7927 AND
IS COMPETENT IN ITS USE.
6.6.1
SETTING THE CO/CO
When running in the service mode, the
boiler will operate both the central heating
and DHW circuits. This is to allow sufficient
time for the setting procedure. It will be
necessary to run sufficient water through
the DHW circuit to ensure that the boiler will
not cycle on low heating demands.
B Refer to section 5.6.1 and ensure that the gas inlet
pressure is correct before continuing.
B To adjust the CO/CO
2
operate the boiler at maximum output.
1. Press and hold down the service button for more than
10 seconds until illuminated.
The blue power indicator will pulse 5 times.
2. Turn central heating control to maximum; the boiler
will then go to maximum output.
The control will resume normal operation
after 15 minutes or if the service button is
pressed for more than a second.
1.
3.
2.
Fig. 75 Setting the boiler
B Refer to table 24 and check the CO/CO
and if required adjust for maximum using a 2.5mm
Allen key.
B Check CO is less than 200ppm.
3. Set the central heating control to minimum.
B The boiler will go to minimum power.
6 720 644 743a (2010/10)
2
it will be necessary to first
at maximum
2
B Measure the CO/CO
and check against table 24
2
below.
If required set the minimum CO/CO
on the gas valve until the correct measurement is set:
– Remove dust cap with flat bladed screw driver.
– Using a 4mm Allen key adjust CO
– Replace the dust cap.
B Check that the CO is less than 200ppm.
B Return to maximum and re-check the CO/CO
If correct, press the service button;
the button will cease to be illuminated and the blue
power indicator will be permanently illuminated.
B Re-assemble and refit boiler case.
MAX
1
2.5 mm
MIN
2
4 mm
Fig. 76 Gas valve adjustment
CO/CO
settings for Greenstar i System
2
CO/CO
should be measured after 10 minutes.
2
Gas type
Natural gas 12i System
Natural gas 15,18 & 24i
System
L.P.G.
NOTE: When checking an existing appliance the
tolerance is ± 0.5.
If checking after cleaning or component replacement
or for adjustment when the reading obtained is
outside the tolerances given above, then the
tolerance is ± 0.2.
CO - less than 200 ppm (0.002 ratio)
Tab. 24 CO/CO
settings
2
SERVICE AND SPARES
via adjuster (2)
2
.
2
.
2
6720643895-66.1Wo
CO
max.
CO
min.
2
2
9.65% ± 0.5
8.65% ± 0.5
9.8% ± 0.5
9.2% ± 0.5
11.0% ± 0.5
10.5% ± 0.5
47
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