49
15.0 Setting the Gas Valve
© Baxi Heating UK Ltd 2014
15.1
Setting the Gas Valve (CO
2
check)
IMPORTANT: The CO
2
must be only be checked and
adjusted to set the valve if a suitable calibrated
combustion analyser is available, operated by a competent
person - see Section 13.1
1. The combustion (CO
2
) may be checked after running the
boiler for several minutes. To do this it is necessary to set the
boiler to ‘Calibration Mode’.
2.
Ensure that all external controls are calling for heat
. The
actual current boiler temperature is shown on the display.
3. Turn both temperature control knobs fully anticlockwise,
then quickly turn the DHW temperature knob
1
/
4
clockwise
twice and back fully anticlockwise (Fig. 101).
4. The display will now alternate between ‘SF’ and the current
boiler temperature and both green LEDs will flash (Figs. 102 &
103).
5. Turn the CH temperature knob fully clockwise. As the knob
is turned the display will change, indicating the fan speed.
6. The display will show ‘00’, indicating maximum rate, then
revert to ‘P ‘ alternating with the current boiler temperature
(Figs 104, 105 & 106).
7. Remove the plug from the flue adaptor test point. Insert the
analyser probe and allow time for the reading to settle (Fig.
107).
The CO
2
should be 9.0% + 0.0 - 0.4 (25)
The CO
2
should be 9.1% + 0.0 - 0.4 (30)
8. It is possible to alter the CO
2
by adjustment of the gas valve.
Remove the plastic cover from the Throttle Adjustment Screw.
At maximum rate the Throttle Adjustment Screw should be
turned, using a suitable hexagon key, until the correct reading is
obtained (Fig. 108). Turning clockwise will reduce the CO
2
.
Anticlockwise will increase th e CO
2
.
9. 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% + 0.0 - 0.4
10. With the boiler on minimum, the ‘Min. Rate’ adjustment
screw must be altered, using a suitable hexagon key, after
removing the cap (Fig. 108). If the CO
2
is reset at either boiler
rate it must be rechecked at the other rate and also adjusted if
required.
11. 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.
12.
Check the Combustion Performance (CO/CO
2
ratio)
.
This must be less than 0.004
.
Selector Switch
Display
Reset
bar
0
1
2
3
4
Central Heating
Temperature Control
Domestic Hot Water
Temperature Control
Fig. 102
Fig. 103
Fig. 104
Fig. 105
Fig. 106
Central Heating
Temperature Control
Domestic Hot Water
Temperature Control
Fig. 101
x 2
Fig. 107
Flue Adaptor Test
Point
Plug
Analyser Probe
Throttle
Adjustment Screw
(cover removed)
Offset
Adjustment Screw
(cap fitted)
Gas Valve
Fig. 108
If the CO
2
is reset at minimum
rate it must be rechecked at
maximum rate again and adjusted
if required. If the CO
2
is reset at
maximum rate it must be
rechecked at minimum rate and
adjusted if required.
Do not turn the adjustment
screws more than 1/8 of a turn at
a time. Allow the analyser reading
to settle before any further
adjustment
Reduce CO
2
at min. rate
Increase CO
2
at min. rate
Reduce CO
2
at max. rate
Increase CO
2
at max. rate
