5. START SEQUENCE
When the gas pressure is nominal, the correct power is supplied to the control panel,
the safety valves are closed, the on/off thermostat emits an “on” signal and all other
boiler values are within the limits, the burner will start when the burner on/off switch is
set to 1.
The start-up sequence is as follows:
A. After switching the system on, the air fan starts at low speed, sometimes after a
short delay.
B. Once the air fan is at nominal speed, the servomotor of the air quantity control
valve (pos. HR2) opens fully. When the servomotor that controls the air quantity
control valve doesn’t make the complete pre-set stroke, the air quantity control
valve will not be sufficiently opened. The burner will be shut off and the system
goes into lockout. An error message is displayed. The air fan will be set to
maximum speed (50 Hz) approximately linear to the air valves to ventilate the
system.
C. If the air quantity control valve is opened the pre-purge cycle starts. During the 30
seconds pre-purge cycle the boiler furnace is ventilated, to clear any remaining
flue gas. During the pre-purge cycle the position of the air quantity control valve
and of the air pressure are checked continuously.
D. At the end of the pre-purge cycle the air fan is set to low speed (+/- 25 Hz) and
the air quantity control valve is positioned to the start/low flame position.
The gas quantity control valve (pos. HR1) controlled by a servomotor is also
positioned to the start/low flame position. The minimum air pressure is checked
during operation by a second air pressure switch (pos. LD2 low).
F. All the air and gas controls are in now in the start position. The next step is to
light the pilot flame. A few seconds after reaching the start position the ignition
transformer is switched on. It make an electrical spark between the ignition
electrodes.
G. After three (3) seconds the pilot gas valve (pos. MK) opens and the spark lights
the gas. After another five (5) seconds the flame monitoring device checks
whether the UV scanner detects a pilot flame. The 5 seconds period during which
the pilot flame is lighted is called the first safety time. At the end of the first safety
time the pilot flame should be burning stable and the electrical spark is switched
off. The flame monitoring unit checks the flame continuously during operation.
If the flame is not formed in the first safety time the flame monitoring unit goes
into lockout and an error message is displayed on the electronic module.
G. If the flame monitoring unit detects the pilot flame, the system continues the
ignition procedure after a short time period. The main safety valves (pos. VA1
and VA2) open to ignite the main flame. The pneumatic gas pressure regulator,
which is mounted on the second safety valve (pos. VA2), makes sure the correct
output gas pressure for the burner load is obtained.
