Servicing Manual
7
Operational sequence
15 s after a regular flame ignition, the flame control unit de-energizes the ignition transformer and the
electrodes stop sparking. The heater goes on operating with self-sustained combustion. The flame control
unit monitors the regular presence of flame by means of the flame sensor. Any abnormal condition, such
as lack of fuel, blockage of air inlet/outlet, dirty or clogged nozzle, that impairs regular combustion has
the effect to close the fuel solenoid valve SV and to interrupt the fuel flow to the burner within the safety
time. The flame control unit will then start a new complete prepurge/ignition sequence, and, should the
problem repeat, the unit will lock out and the aftercooling sequence will start.
Restart sequence
If the flame shuts down for any reason, the flame control unit repeats the whole start sequence, consisting
of the prepurge and the ignition sequences. If there is no flame signal within the safety time T4, the
control unit goes to lock-out and the red lamp on the control panel lights up. If, on the contrary, a small
flame signal is detected within the safety time, the control unit repeats the start sequence. The whole
sequence will be repeated 3 times maximum and then the unit will definitely lock out. A maximum
number of 3 ignition tries has been fixed to avoid that excessive smoke is produced during the repeated
starting sequences. This effect could occur when the fuel tank is almost empty and the suction hose
contains fuel and air mixed, or when the nozzle is partially blocked or damaged, and therefore the
pressurized fuel is incorrectly sprayed.
Aftercooling sequence
During this time the heater is subjected to a cooling cycle to avoid excessive overheating of materials
and components that could occur if the motor/fan suddenly stopped. This sequence is also very important
from the point of view of efficiency, as all the residual heat that accumulates in the combustion chamber
can be recovered and sent in the space to be heated.
For safety reasons, it has been established that the high voltage ignition transformer must be energized
during the aftercooling time. By doing this, any small fuel residuals coming from the solenoid valve SV
will burn completely and will not accumulate inside the combustion chamber. Any explosion risk or
abnormal heat release during future ignition sequences is therefore prevented.
The aftercooling time is factory set and independent of the action of a limit control or similar devices on
the combustion chamber. The aftercooling time lasts about 1 minute and 45 seconds.
Lock-out sequence
In the event of flame shut down due to lack of fuel or to another reason (see also the par. “SAFETY
OPTIONS IN CASE OF ABNORMAL OPERATION”) the flame control unit will put the heater in a
safety condition starting the lock-out sequence. During this sequence the fuel solenoid valve SV is
immediately closed within the safety time T4 (< 1s) and then an aftercooling cycle will start to cool the
surfaces of the combustion chamber. The ignition transformer is powered, and therefore a spark is
produced by the electrodes, during the aftercooling cycle as described above.
Reset sequence
The unit can be reset by pushing the red reset pushbutton with integral warning lamp on the control panel.
For safety reasons, reset will only be possible after about 30 s from lock-out. Also in the event of
electrical supply failure/restoration, reset will only be possible after 30 s approximately.
