Setting the gas valve (CO
2
)
Important
The CO
2
must be only checked and adjusted to set the valve if a
suitable calibrated combustion analyser is available, operated by a
competent person.
See
Annual Servicing, page 53
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 "Calibra
tion 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 in quick succession (within 2
seconds).
4. "304" will appear in the display screen.
5. Turn the left hand knob fully clockwise. "100" will appear in the display
screen, indicating maximum output.
1
Combustion test point
2
Incoming air for combustion test point
A
Throttle Adjustment Screw
B
Offset Adjustment Screw
6. Remove the plug from the flue sampling test point. Insert the analyser
probe and allow sufficient time for the reading to settle.
Potterton
Assure Combi
25
30
CO
2
% (maximum)
9.0 + 0.3 – 0.2
9.0 + 0.3 – 0.2
7. 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.
Turning clockwise will reduce the CO
2
.
Turning anticlockwise will increase the CO
2
.
8. The CO
2
must then be checked at minimum rate. Turn the left hand
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.
Potterton
Assure Combi
25
30
CO
2
% (minimum)
8.5 + 0.1 — 0.4 8.5 + 0.1 — 0.4
9. With the boiler on minimum, the Offset Adjustment Screw must be al
tered, using a suitable hexagon key, after removing the cap.
Turning clockwise will increase the CO
2
.
Turning anticlockwise will reduce the CO
2
.
10. The calibration function is maintained for 20 minutes unless the maxi
mum central heating temperature is exceeded. The function can be
disabled at any time by turning the right hand knob.
11. Check the combustion performance (CO/CO
2
ratio). This must be less
than 0.004.
Fig.61
Setting the gas valve
Reset
bar
0
1
2
3
4
R
Min
M
a
x
M
a
x
Min
M
a
x
Min
M
a
x
Min
[
M
a
x
Min
M
a
x
Min
PN-0000376
R
1
2
E
V1
E
V
2
P
. OUT
1 2
3
4
VEN
T
R
Q
AD
J.
P
.R
. A
DJ
.
A
B
9 Maintenance
60
7678846 - A - 22052017
