24
16. Gas change
modalities
The gas change modalities is different depending on the kind of gas valve installed:
a) gas valve SIEMENS model VDU 11 (figure 14);
b) gas valve SIGMA model 848 (figure 14a).
Carry out the following operations in the given sequence:
1) calibration of the maximum heat output.
Check that the CO
2
measured on the flue, with the
boiler operating at the maximum heat output, is the same as that shown in table 1. Otherwise, turn
the regulation screw (V) on the gas valve.
a) gas valve SIEMENS model VDU 11 (figure 14):
turn the screw clockwise to increase the
concentration of CO
2
and anticlockwise to reduce it;
b) gas valve SIT model SIGMA 848 (figure 14a):
turn the screw clockwise to reduce the
concentration of CO
2
and anticlockwise to increase it;
2) calibration of the reduced heat output.
Check that the CO
2
measured on the flue, with the boiler
operating at the minimum heat output, is the same as that shown in table 1. Otherwise, turn the
regulation screw (K) on the gas valve. Turn the screw clockwise to increase the concentration of
CO
2
and anticlockwise to reduce it;
0310_01
14
Figure 14a
Pi:
Gas supply pressure connection point
PO/Pout:
Gas pressure to burner connection point
P:
Pressure connection point for measurement of the OFFSET
Pl:
Air signal input from fan
V:
Gas flow adjuster screw
K:
OFFSET adjuster screw
Figure 14
020523_0700
GAS VALVE SIEMENS
MODEL VDU 11
GAS VALVE SIT
MODEL SIGMA 848
