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15.0 Combustion Check
© Baxi Heating UK Ltd 2008
15.1 Checking the CO
2
IMPORTANT: The CO
2
must only be checked and
adjusted if a suitable calibrated combustion analyser is
available.
1. The combustion (CO
2
) may be checked using a suitably
calibrated analyser after running the boiler for several
minutes.
2. To do this it is necessary to set the boiler to ‘Calibration
Mode’.
3. Ensure that all external controls are calling for heat. The
actual current boiler temperature is shown on the display.
4. Turn both temperature control knobs fully anticlockwise,
then quickly turn the DHW temperature knob
1
/
4
clockwise
twice and back fully anticlockwise (Fig. 105).
5. The display will now alternate between ‘SF’ and the
current boiler temperature and both green LEDs will flash
(Figs. 106 & 107).
6. Turn the CH temperature knob fully clockwise. As the
knob is turned the display will change, indicating the fan
speed.
7. The display will show ‘00’, indicating maximum rate, then
revert to ‘P ‘ alternating with the current boiler temperature
(Figs 108, 109 & 110).
8. Remove the plug from the flue adaptor test point. Insert
the analyser probe and allow time for the reading to settle
(Fig. 111).
The CO
2
should be 8.7% ± 0.2
9. It is possible to alter the CO
2
by adjustment of the gas
valve. Remove the plastic cover from the ‘Max Rate’
adjustment screw. At maximum rate the ‘Max. Rate’
adjustment screw should be turned, using a suitable
hexagon key, until the correct reading is obtained (Fig. 112).
Turning clockwise will reduce the CO
2
. Anticlockwise will
increase the CO
2.
10. The CO
2
must then be checked at minimum rate. Turn
the CH temperature knob fully anticlockwise. As the knob is
turned the display will change, indicating the fan speed.
When the display reads ‘ 0’ the boiler runs at minimum rate.
The CO
2
should be 8.4% ± 0.2.
11. With the boiler on minimum, the ‘Min. Rate’ adjustment
screw must be altered, using a suitable hexagon key, after
removing the cap (Fig. 112). If the CO
2
is reset at either
boiler rate it must be rechecked at the other rate and also
adjusted if required.
12. The ‘Calibration Function’ is maintained for 20 minutes
unless the maximum CH temperature is exceeded. The
function can be disabled at any time by turning the DHW
knob.
Selector Switch
Display
Reset
1
2
3
4
5
PM
7
8
9
10
11
12
1
2
3
4
5
AM
7
8
9
1
0
11
12
0
bar
0
2
3
4
Central Heating
Temperature Control
Domestic Hot Water
Temperature Control
Fig. 106
Fig. 107
Fig. 108
Fig. 109 Fig. 110
Central Heating
Temperature Control
Domestic Hot Water
Temperature Control
Fig. 105
x 2
Fig. 111
Max Rate
Adjustment Screw
(cover removed)
Min Rate
Adjustment Screw
(cap fitted)
Gas Valve
Fig. 112
Flue Adaptor Test
Point
Plug
Analyser Probe