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Check that the air pressure witch functions properly with burner operating at 1st flame only, increase the
regulating value until it reaches intervention point and the burner should go to shut down. To unlock the burner,
press the special push-button and return the pressure switch regulator to a sufficient value in order to measure
the air pressure existing during the pre-ventilation phase.
17) The pressure switches which control the gas pressure (minimum and maximum) have the job of stopping the
burner functioning when the gas pressure is not within the values specified. From the specific functions of the
pressure switches, it is evident that the pressure which controls the minimum pressure must make use of the
contact, which is closed, when it measures a pressure which exceeds that at which it has been set.
The maximum pressure switch must make use of the contact, which is closed, when it measures a pressure
below that at which it has been set.
The minimum and maximum gas pressure switches should be regulated during the burner’s general inspection
and should be in function with the pressure found each time.
The pressure switches have been electrically connected in series and therefore the intervention (by this we mean
the opening of the circuit) of any one of the gas pressure switches does not allow the control box to be inserted.
It must be pointed out that the intervention (by this we mean the opening of the circuit) of any one of the pressure
switches when the burner is operating (flame lit) determines the immediate arrest of the burner.
During the burner’s general inspection, check the correct functioning of the pressure switches. By operating the
respective regulating devices, it is possible to control the pressure switch’s intervention (opening of circuit) which
causes the burner’s arrest.
18) Check the efficiency of the flame detector (ionisation electrode) by detaching the wire coming from the electrode
and then turning on the burner.
The control box should complete its cycle and, two seconds after the ignition flame is formed, it should block
(“shut down”).
This test should also be carried out when the burner is already operating.
By detaching the wire that comes from the ionisation electrode, the control box should immediately block (“shut
down”). (See also Chapter on “Maintenance”).
In the case of a UV Cell, extract it by sliding it out of its seat about one minute after ignition.
It will not be able to “see” the ultraviolet radiation emitted by the flame and therefore the relative relay will de-
energise. The burner will come immediately to a standstill.
Even the slightest greasiness will compromise the passage of the ultraviolet rays to the UV photoelectric cell
bulb, thus preventing the sensitive internal element from receiving the quantity of radiation necessary for it to
function correctly.
Should the bulb be fouled by light oil, fuel oil, etc., it is indispensable to clean it thoroughly.
It should be pointed out that even by simply touching the bulb with the fingers, it is possible to leave a slight
greasiness which could compromise the working of the UV photoelectric cell. The UV Cell does not “see”
daylight or light from an ordinary lamp.
It is possible to verify its sensibility with a flame (or cigarette lighter or a candle) or with the electric spark that
occurs between electrodes in an ordinary ignition transformer.
To ensure that the UV Cell works properly, its current value should be sufficiently stable so as to not fall below the
minimum value required for the specific control box (this value is shown in the electrical diagram).
It may be necessary to search experimentally for the best position by sliding (axial or rotation movement) the
body that contains the photoelectric cell in respect to the fastening clamp. An inspection can be carried out by
inserting a microammeter, with an adequate scale, in series to one of the two UV photoelectric cell connection
wires. It is obviously necessary to respect the polarity ( + and - ).
The control box can only be unblocked by pressing the relevant push-button.
Check the efficiency of the “shut down” device at least twice.
19) Check the efficiency of the boiler thermostats and pressure switches (this should result in the burner coming to
a standstill).
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