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15) Then turn off the switch to ignite the burner. When the burner is lit, with the second flame, immediately check
the gas supply, first visually and then by reading the meter. Depending on these checks, gas delivery can be
adjusted, if necessary, to the value required in each specific case (boiler power), remembering that methane
develops 8550 kcal/m
in two readings taken exactly one minute apart. Multiply this value by sixty to obtain the delivery in 60 minutes,
i.e. one hour. The delivery measured is taken as the actual value if the meter measures a pressure of less than
400 mm H
O, otherwise the value calculated must be multiplied by the correction coefficient (see the chapter
2
"Reading the meter"). Then, multiply the hourly delivery (m
the power delivered in kcal/h. This value must be equal to, or very close to that required by the boiler (lower
heating power for methane = 8550 kcal/m
case. To avoid possible damage to the boiler, do not keep the burner operating if the flow exceeds the maximum
allowed. The burner should therefore be stopped immediately after the two meter readings are taken.
16) Use suitable instruments to check that combustion occurs correctly (CO
0.1%). To optimise combustion and for good flame stability (no flicker), the combustion head regulator may
have to be adjusted (see the chapter "Regulating the air to the combustion head"). Normally the air gap between
the disc and the head must be reduced when working with a reduced fuel delivery. The gap must be opened
proportionally when the burner is working with at higher fuel delivery. When the flame disc is adjusted, normally
it is also necessary to correct the position of the air shutter of the first and second flames, then, check that
ignition occurs correctly.
17) The air pressure switch is used to put the unit on safety (cut-out) if the air pressure is not at the required level.
The pressure switch must therefore be adjusted to cut-in, closing the contacts (which must be closed during
operation), when the air pressure in the burner reaches a sufficient level. The pressure switch connection
circuit provides for automatic control, therefore the contact must be able to remain closed when at rest (fan
stopped and lack of air pressure in the burner) to actually enable this condition, otherwise the command and
control unit will not be activated (the burner will stay off). If a contact required to remain closed during the
working cycle is not closed, the unit will only complete part of its cycle and then shut down "cut-out" without
activating the ignition transformer or the gas valves. To check that the air pressure switch is working properly,
increase the setting with the burner on first flame only, until the switch cuts in, which must result in immediate
burner shut down "cut-out". Reset the burner by pressing the special pushbutton and bring the setting on the
pressure switch to a sufficient value for detecting the air pressure present during the pre-ventilation phase.
18) The gas pressure pressure switches (minimum and maximum) are used to prevent the burner from working
when the gas pressure is outside the required limits. According to the specific function of the pressure switches,
it is clear that the the minimum pressure control switch must have its contact closed when it detects a pressure
above its setting. The maximum pressure switch must have its contact closed when it detects a pressure below
its setting. The maximum and minimum gas pressure switches must therefore be set at the time of burner
testing, according to the pressure measured in each case. The pressure switches are electrically connected in
series so that when the gas pressure switches intervene (when the circuit opens) the unit is not turned on.
Intervention (i.e. opening of a circuit) of any pressure switch when the burner is working (flame lit), causes the
burner to stop immediately. When testing the burner, it is essential to check that the pressure switches are
working properly. Pressure switch intervention (opening of the circuit), which must shut down the burner, is
checked by operating the respective regulation devices.
1
9) Safety checks Check the efficiency of the UV photocell flame detector.
At least one minute after ignition, remove the photocell from its seat. When the UV photocell is removed from
its seat it can no longer "see" the ultraviolet radiation emitted by the flame, therefore the relative relay is de-
activated. The burner immediately shuts down "cut-out". Even slight oiliness greatly affects the passage of UV
rays to the bulb in the UV photocell, preventing the sensitive internal element from receiving the amount of
radiation required for the unit to work properly. If the bulb becomes fouled by gas oil, fuel oil, etc., it must be
cleaned properly. Even touching the bulb with a finger can leave enough oiliness to affect UV photocell operation.
The UV cell does not "see" daylight or light from a normal lamp. Its sensitivity can be checked with a flame
(lighter, candle) or an electric spark between the electrodes of an ordinary ignition transformer.
To ensure that the unit works properly, the current on the UV cell must be sufficiently stable and must not fall
below the minimum value required for the specific unit. This value is given in the wiring diagram. The best
position may have to be found by experimenting, by sliding (axial movement or rotation) the body containing the
photocell on the clamping bracket. The unit can be checked by connecting a micro-ammeter, with a suitable
scale, in series with one of the two UV photocell cables. Obviously the polarity must be respected (+ and -).
The unit can only be reset manually by pressing the special pushbutton (reset). The cut-out efficiency check
must be carried out at least twice. Check the efficiency of boiler thermostats or pressure switches (their
intervention must shut down the burner). Check the efficiency of air and gas pressure switches.
. With the burner on at the 2
3
). Adjust the flow regulator for the 2nd flame to suit each specific
3
nd
flame, check the gas delivery by calculating the difference
3
/h) by the heating power of the gas, thereby obtaining
= 8 - 10% for methane / CO max.
2
23
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