19
17) The minimum thermostat closes when the fuel in the pre-heater reaches the set temperature. Closing of the
minimum thermostat does not cause the burner command and control unit to be activated immediately.
This unit is activated by the regulation thermostat (switching contact) when it turns off the heating elements
due to the fuel reaching the temperature set on the regulating thermostat. The burner starts, provided the
boiler and safety thermostats and pressure switches are closed, but only when the heating elements have
been disconnected and the maximum pre-heating temperature has been reached. While the burner is working
an auxiliary relay (in series with the minimum thermostat) prevents the burner from stopping when the regulation
thermostat switches the contact to turn on the heating elements again (see wiring diagram).
Ignition of the burner begins with activation of the command and control unit. The program provides for pre-
ventilation of the combustion chamber, while pre-circulating hot oil at low pressure, throughout the fuel circuit
of the burner. The burner ignites as described in the previous chapter (see “Description of operation”), with the
burner igniting at minimum power.
18) Once the burner is operating on 1
st
flame, the air regulated as described in the specific instructions, to ensure
the quantity required for good combustion (see BT 8653/1). Preferably, the amount of air for the first flame
should be a little lean in order to ensure proper ignition, even under the most demanding conditions.
19) Once the air has been regulated for the first flame, the burner is stopped by turning the main switch off, and
the terminals of the thermostat terminal board of the second flame are connected to one another.
This connection makes it possible for the second flame to be activated.
20) The unit is switched on again and the program governed by the cycle relay automatically switches it to the
second flame.
21) With the unit thus working the second flame is regulated, operating as described in the specific instructions, to
the quantity required to ensure good combustion. Combustion must be checked using special instruments. The
air regulator must be positioned in order to give a percentage of carbon dioxide (CO
2
) in the fumes varying from
a min. 10% to a max. 13%. Remember that for good adjustment, the water in the system must be at the correct
temperature and the burner must have been working for at least fifteen minutes.
If no suitable instruments are available, this must be based on the colour of the flame. It is advisable to regulate
the flame until it has a light orange colour. A red flame should be avoided as it indicates the presence of smoke,
while a white flame indicates too much air. Make sure the pre-heater thermostat settings do not give rise to any
problems (poor combustion, presence of smoke, formation of gas in the pre-heater, etc.). If necessary, increase
or decrease these settings, remembering that the regulation thermostat must be set at a temperature of about
15 - 20° C higher than the setting on the minimum thermostat. The minimum thermostat must close at the
minimum temperature in order to achieve good combustion (viscosity at the nozzle of about 2° E).
See the viscosity – temperature diagram for the type of oil used.
AIR REGULATION AT THE COMBUSTION HEAD (see BT 8608/1)
The combustion head is fitted with a regulation device that closes (moves forward) or opens (moves back) the air
gap between the disc and the head. In this way, when the gap is closed, high pressure can be obtained upstream
of the disc, even at low flow rates. The high speed and turbulence of the air allows it to penetrate the fuel better,
creating an excellent mixture and providing a stable flame. It may be essential to have a high air pressure upstream
of the disc to prevent the flame from flickering. This is practically indispensable when the burner is working in a
pressurised firebox and/or at high thermal loads. Therefore, it is clear that the device which shuts off the air at the
combustion head must be positioned in such a way as to always keep the air pressure behind the disc at a
significantly higher level. It is advisable to adjust it in order shut off the air to the head, in order to cause the air lock
that controls the intake for the fan to open considerably. Obviously, this must be checked when the burner is
working at the maximum delivery required. In practice, regulation must begin using the device that closes the air
to the combustion head in an intermediate position, and the burner must be ignited to allow regulation as explained
above. When the maximum delivery required has been reached, the position of the device that shuts off the air to
the combustion head must be corrected, by moving it forward or back to provide an adequate air flow with the air
intake shutter considerably open. When reducing the air passage in the combustion head, care must be taken not
to close it altogether. Make sure it is perfectly centred in relation to the disc. If it is not properly centred on the disc,
poor combustion and overheating of the head could occur, resulting in its rapid deterioration.
This check can be made by watching the LED on the back of the burner and then tightening the screws that lock
the regulator for the air at the combustion head, in position.
N.B. Make sure ignition takes place correctly because, if the regulator has moved forward the speed of the air
coming out may be so high that it makes ignition difficult. If this should occur, move the regulator further
back a little at a time, until a position is reached where ignition occurs regularly, and accept this as the
regulator’s permanent position. It is preferable to limit the amount of air, for the 1st flame, to as little as
possible, to ensure ignition, even under the most demanding conditions.
