31
INS
TALLER
US
ER
MAINTEN
AN
CE TECHNI
CI
AN
3.6 ADJUSTMENT OF THE AIR-GAS
RATIO.
Attention:
the verification operations of the CO
2
must be carried out with the casing mounted,
while the gas valve calibration operations must
be carried out with the casing open and removing
the voltage from the boiler.
Calibration of the minimum CO
2
(minimum
heating power).
Enter the chimney sweep phase without
withdrawing domestic hot water and take the
selector switches to minimum (turn them in an
anti-clockwise direction until "0" is seen on the
display). to have an exact value of CO
2
in the flue
gases the technician must insert the sampling
probe to the bottom of the sample point, then
check that the CO
2
value is that specified in the
table, otherwise adjust the screw (3 Fig. 3-3) (Off-
Set adjuster). To increase the CO
2
value, turn the
adjustment screw (3) in a clockwise direction and
vice versa to decrease it.
Calibration of the maximum CO
2
(nominal
central heating power).
On completion of the adjustment of the
minimum CO
2
keeping the chimney sweep
function active, take the heating selector switch
to maximum (turn it in a clockwise direction
until “99” is seen on the display). To have an exact
value of CO
2
in the flue gases the technician must
insert the sampling probe to the bottom of the
sample point, then check that the CO
2
value is
that specified in the table, otherwise adjust the
screw (12 Fig. 3-3) (Gas flow adjuster).
To increase the CO
2
value, turn the adjustment
screw (12) in a clockwise direction for the 8205
gas valve and anticlockwise for the 848 gas and
vice versa to decrease it.
At every adjustment variation on the screw 12 it
is necessary to wait for the boiler to stabilise itself
at the value set (about 30 sec.).
CO
2
at nominal
output
(central heating)
CO
2
at minimum
output
(central heating)
G 20
9.50% ± 0.2
8.90% ± 0.2
G 30
12.20% ± 0.2
11.10% ± 0.2
G 31
10.50% ± 0.2
10.20% ± 0.2
3.7 CHECKS FOLLOWING
CONVERSION TO ANOTHER TYPE
OF GAS.
After making sure that conversion was carried
out with a nozzle of suitable diameter for the
type of gas used and the settings are made at the
correct pressure, check that the burner flame is
not too high or low and is stable (does not detach
from burner).
N.B.:
all boiler adjustment operations must
be carried out by a qualified technician (e.g.
Authorised After-sales Service).
