76
GB
Burner control
Ignition
On closure of the heat request contact and when the correct status of the air pressure contact has been verified,
the fan motor is inserted and the air damper total opening is controlled.On reaching total opening of the damper
and switch-over of the air pressure switch contact has been verified, the pre-ventilation time starts during which
the flame amplifier test is performed along with components associated to safety functions. An amplifier fault that
corresponds to a flame present condition or the breakdown of a component that ensures a safety function pre-
vents the start of the ignition sequence.
At the end of the pre-ventilation time, the air damper is positioned in the first stage ignition position with conse-
quent activation of the ignition transformer (pre-ignition phase).On expiry of the latter, safety time timing starts,
during which the first stage solenoid valve is inserted.
On detection of flame signal presence, the ignition transformer remains inserted until the end of the safety time
and, after appropriate timing, functioning regulation is enabled, following the commands supplied by the external
regulator.If there is no ignition during the safety time, the appliance is blocked and the voltage is definitively re-
moved to the first stage solenoid valve and the ignition transformer. Post-ventilation is performed with the damper
totally open, at the end of which the air damper is closed completely.
Functioning principle
According to the device to which the air damper activation servo-control is interlocked, there are two types of bur-
ner working: two-stage progressive if the control element is the all-or-nothing- type (ON/OFF), continuous flame
modulation if the device is the modulating type
FUNCTIONING CYCLE
Two-stage progressive functioning
It is that obtained with a normal open-close (ON/OFF) boiler thermostat (or pressure switch), for which the servo-
control makes the air damper assume two possible positions: the minimum (1st stage) and maximum opening
(2nd stage). It is called two-stage progressive functioning because the passage from one to the other takes place
gradually and linearly without jumps.The following characteristic phases can be noted in the representative dia-
gram:
a) Stop sequence: with the burner off, the air damper is in the closure position in order to prevent that air from
entering and cooling the combustion chamber of the boiler and flue.
b) Pre-ventilation sequence: the air damper goes to maximum opening with successive return to partial closure
M
2nd stage
1st stage
start-up
air
gas
1s max
functioning
time