42
c)
It could happen that the ionisation current is held up by the discharge current of the ignition transformer
(the two currents have to run the same course on the burner’s hearth) and so the burner goes to “shut
down” due to insufficient ionisation.
This can be remedied by inverting the input (220V side) of the ignition transformer (charge the places of
the two wires that take voltage to the transformer).
A shut down can also be caused by the burner’s casing not being properly grounded. The minimum
value of the ionisation current to ensure the working of the control box is shown on the specific electrical
diagram.
To check the ionisation current, connect a micro-ammeter with an adequate scale “in series” to the
ionisation circuit.
The high isolation wire that comes from the electrode must be inserted to the negative (sign - ) of the
micro-ammeter.
11)
With the burner operating at a minimum, immediately check visually the entity and appearance of the flame and,
if necessary, proceed with correcting it by operating the regulators of the gas and air delivery (see points 7 and 8).
Subsequently, check the quantity of gas delivered by reading the meter. (See point 15).
If necessary, correct the gas and relative combustion air delivery by operating as previously described (points 7
and 8).
Note : To regulate the gas valve and the electric motor which commands the air shutter, refer to the specific
instructions shown in the following pages.
12)
After regulating the 1st flame, turn off the burner, open the main switch and close the electric circuit which
commands insertion of the 2nd flame (connect the terminals n° 19 and n° 26, see electrical diagram).
13)
Open the manual gas flow regulator to the amount considered necessary for the 2nd flame (main flame).
To regulate the gas valve and the electric motor which commands the air shutter, see specific instructions
contained in the following pages.
14)
Now turn on the burner again by closing the main switch and that of the control box.
The burner starts up and automatically inserts the 2nd flame (main flame).
Immediately check visually the entity and appearance of the flame and proceed, if necessary, with correcting
gas and air delivery, as described in points 7 and 8.
15)
With the burner operating at nominal delivery, proceed with measuring the gas output by taking two readings -
the second one exactly one minute after the first one.
The difference between the two is multiplied by sixty in order to obtain the output for sixty minutes (one hour).
The output measured is considered the actual value if the meter reads a pressure below 400 mm.W.C. ; if it is
more than this, the value read must be multiplied by a correction coefficient (see Chapter “Reading the Meter).
Subsequently, multiply the delivery per hour (m
3
/h) by the gas calorific value to obtain the potentiality delivered in
Kcal/h; this should correspond or be very near to that requested for the boiler (low calorific value for methane gas
= 8550 Kcal/m
3
).
It may be necessary to adjust considerably the flow regulator for the 2nd flame in order to regulate it correctly.
Do not allow the burner to operate if the output exceeds the maximum allowed for the boiler, to avoid possible
damage to it; it is timely to stop the boiler immediately after having taken the two meter readings.
Then control combustion with the appropriate instruments.
For a correct air/gas ratio, the percentage of Carbon Dioxide (CO
2
) for methane gas should be from at least 8%
at minimum burner delivery to an optimum value of 10% for maximum delivery. We advise against exceeding the
value of 10% to avoid operating with a rather limited excess of air which could cause (variation in atmospheric
pressure, presence of dust particles in fan’s air ducts) a considerable amount of Carbon Monoxide (CO).
It is indispensable to check, with the appropriate instruments, that the Carbon Monoxide (CO) present in the
smoke does not exceed the maximum level permitted of 0,1%.
16)
The air pressure switch has the job of stopping the gas valves opening if the air pressure is not at a correct value.
Therefore, the air pressure switch must be regulated in such a way as to intervene by closing the contact
(foreseen to be closed while working) when the air pressure in the burner has reached a sufficient level.
The pressure switch is self-controlled and therefore it must close the contact, which is foreseen to be closed at
rest, (fan stops and consequently there is an absence of air pressure in the burner) ; if it does not, the control box
will not be inserted (the burner remains at a standstill). It must be specified that if the contact is not closed
during working, the control box will carry out its cycle, but the ignition transformer will not be inserted and the gas
valves will not open. Consequently, the burner will go to shut down.
