Baxi Potterton BBU 15 HE manual Setting the Gas Valve CO2 check

Flue Sampling

Point

Display

Control	Fig. 56
Knobs

Fig. 57 Fig. 58

11.0Setting the Gas Valve

11.1Setting the Gas Valve (CO2 check)

IMPORTANT: The CO2 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 (CO2) 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 ).

Fig. 59

Fig. 60

Min Rate

Adjustment Screw

(cap fitted)

Reduce CO2	Increase CO2
at min. rate	at min. rate

Fig. 61

Max Rate

Adjustment Screw

(cover removed)

Reduce CO2	Increase CO2
at max. rate	at max. rate

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 CO2 should be 9.3% ± 0.2

8.It is possible to alter the CO2 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 CO2. Anticlockwise will increase the CO2.

9.The CO2 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 CO2 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 CO2. Clockwise will increase the CO2.

Fig. 62

If the CO2 is reset at minimum rate it must

be rechecked at maximum rate again and adjusted if required. If the CO2 is reset at

maximum rate it must be rechecked at minimum rate and adjusted if required.

© Baxi Heating UK Ltd 2009

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/CO2 ratio. This must be less than 0.004.

33