Baxi Potterton BBU 15 HE - Manual (Page 33)

33
© Baxi Heating UK Ltd 2009
11.0 Setting the Gas Valve
11.1 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 9.1
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 control knobs fully anticlockwise, then quickly
turn the right hand knob 1 /
4
clockwise twice and back fully
anticlockwise (Fig. 56).
4. The display will now alternate between ‘SF’ and the
current boiler temperature and both green LEDs will flash
(Figs. 57 & 58).
5. Turn the left hand 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. 59, 60 & 61 ).
7. Remove the plug from the flue sampling test point. Insert
the analyser probe and allow sufficient time for the reading
to settle (Fig. 56).
The CO
2
should be 9.3% ± 0.2
8. 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. 62).
Turning clockwise will reduce the CO
2
. Anticlockwise will
increase the CO
2
.
9. The CO
2
must then be checked at minimum rate. Turn
the left hand knob fully anti-clockwise. 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 8.2% ± 0.2
10. With the boiler on minimum, the ‘Min. Rate’ adjustment
screw must be altered, using a suitable hexagon key, after
removing the cap (Fig. 62). Turning anti-clockwise will reduce
the CO
2
. Clockwise will increase the CO
2
.
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 right
hand knob.
12. Check the CO/CO
2
ratio. This must be less than 0.004.
Control
Knobs
Display
Flue Sampling
Point
Max Rate
Adjustment Screw
(cover removed)
Min Rate
Adjustment Screw
(cap fitted)
Fig. 56
Fig. 57 Fig. 58
Fig. 59
Fig. 60 Fig. 61
Fig. 62
Reduce CO
2
at min. rate
Increase CO
2
at min. rate
Reduce CO
2
at max. rate
Increase CO
2
at max. rate
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.