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6.5.3
Minimum gas pressure switch
The purpose of the minimum gas pressure switch is to prevent
the burner from operating in an unsuitable way due to too low gas
pressure.
Adjust the minimum gas pressure switch (Fig. 32) after having
adjusted the burner, the gas valves and the gas train stabiliser.
With the burner operating at maximum output:
–
install a pressure gauge downstream of the gas train stabilis-
er (for example at the gas pressure test point on the burner
combustion head);
–
choke slowly the manual gas cock until the pressure gauge
detects a decrease in the pressure read of about 0.1 kPa
(1 mbar). In this phase, verify the CO value which must al-
ways be less than 100 mg/kWh (93 ppm).
–
Increase the adjustment of the gas pressure switch until it in-
tervenes, causing the burner shutdown;
–
remove the pressure gauge and close the cock of the gas
pressure test point used for the measurement;
–
open completely the manual gas cock.
1 Kpa = 10 mbar
WARNING
6.5.4
PVP pressure switch kit
Adjust the pressure switch for the valve leak detection control de-
vice (PVP Kit)(Fig. 35), if present, according to the instructions
supplied with the Kit itself.
6.6
Steady-state operation
Once the start-up cycle is completed, the servomotor command
moves on to the thermostat/pressure switch that controls the
pressure or the temperature in the boiler.
If the temperature or the pressure is low the burner progres-
sively increases the output as far as the MAX value.
If the temperature or the pressure increases as far as the
opening of the thermostat/pressure switch, the burner pro-
gressively reduces the output as far as the MIN value.
6.7
Ignition failure
If the burner does not switch on, there is a lockout within 3s of the
electrical supply reaching the gas valve.
It may be that the gas does not arrive at the combustion head
within the safety time of 3 s.
In this case, increase gas delivery upon ignition.
The arrival of the gas at the pipe coupling is shown on the pres-
sure gauge of Fig. 38 at page 39.
6.8
Burner flame goes out during operation
If the flame accidentally goes out during operation, the control
box carries out a recycle (i.e. it repeats the start-up phase once,
and makes a further ignition attempt).
If the flame is still absent, the control box goes into lockout.
Start-up, calibration and operation of the burner
The burner switches off when the request for heat is lower
than the heat supplied by the burner at MIN output.
The thermostat/pressure switch TL opens and the control
box carries out the switching off phase.
The damper closes completely to reduce thermal disper-
sions to a minimum.
In the event of a burner lockout, more than two
consecutive burner reset operations could cause
damage to the installation. On the third lockout,
contact the Aftersales Service.
WARNING
If further lockouts or burner faults occur, interven-
tions must only be made by qualified, authorised
personnel (as indicated in this manual, and in
compliance with the laws and regulations current-
DANGER
ly in force).
35
GB
D3855
Fig. 34
Fig. 35
D3855
20155480
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