14
BURNER OPERATION
BURNER START-UP (A)
• 0s:
Closure of thermostat/pressure
switch TL.
• 2s:
Start of electrical control box pro-
gramme. Servomotor starts: rotate to
the left by 90°, i.e. until the contact
intervenes with cam I (D)p. 10.
• 26s:
The air damper arrives to the MAX.
output position.
The fan motor starts up.
Start of the pre-purging phase.
• 57s:
The servomotor rotates towards the
right, as far as the angle set on cam III
(D)p. 10 for MIN. output.
• 77s:
The air damper and the gas butterfly
valve adopt the MIN output position
(with cam III)(D)p.10 at 15°).
• 92s:
Ignition electrode strikes a spark.
The safety valve VS opens, along with
the adjustment valve VR, quick open-
ing. The flame is ignited at a low out-
put level, point A.
Delivery is then progressively
increased, with the valve VR opening
slowly up to MIN. output, point B.
• 94s:
The spark goes out.
• 118s: The start-up cycle ends.
STEADY STATE OPERATION (A)
Burner without modulating operation kit
Once the start-up cycle is completed, the servo-
motor command moves on to the thermostat/
pressure switch TR that controls the pressure or
the temperature in the boiler, point C.
(The electrical control box still continues to
check the presence of the flame and the correct
position of the air and gas pressure switches).
• If the temperature or the pressure is low, so
the thermostat/pressure switch TR is in the
output request position, the burner progres-
sively increases the output up to the MAX
value (tract C-D).
• If the temperature or the pressure increases
until the commutation of TR, the burner pro-
gressively reduces the output up to the MIN
value (tract E-F). And so on.
• The burner locks out when demand for heat is
less than the heat supplied by the burner at
min. output, (section G-H). The thermostat/
pressure switch TL opens, and the servomo-
tor returns to the angle 0°. The damper closes
completely to reduce thermal dispersions to a
minimum.
Burner with modulating operation kit
See the handbook enclosed with the regulator.
IGNITION FAILURE (B)
If the burner does not switch on, the gas valve
goes into lockout within 3s of the opening.
BURNER FLAME GOES OUT DURING OPER-
ATION
If the flame goes out by accident during the
operation, the burner goes into lockout within
1s.
(A)
(B)
STANDARD IGNITION
(n° = seconds from the moment 0)
IGNITION FAILURE
D3857
D3858
