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tact when the air pressure in the burner reaches a sufficient
value. The pressure switch connection circuit provides for auto
control so it necessary for the contact to be actually closed
when the fan is stopped (no air pressure in burner). If it is not
the command and control equipment will not go on (the burner
stays stopped). If the air pressure switch does not detect pres
-
sure greater than that calibrated, the equipment runs through
its cycle but does not switch on the ignition transformer and
does not open the gas valves and so the burner “locks-out”.
To ensure correct working of the air pressure switch you must,
with burner on and with first flame only, increase the regula
-
tion until it is triggered and immediately “locks-out” the burner.
To release the burner, press the release button and adjust the
pressure switch to a sufficient level to detect the existing air
pressure during the preventilation stage.
15) The control pressure switches for the gas (minimum) are to
prevent the working of the burner when the pressure of the
gas is not as provided for. It is clear from the specific function
of the pressure switches that the control pressure switch for
minimum pressure must make use of the contact that is closed
when the pressure switch detects a pressure greater than that
for which it is regulated. The adjustment of the minimum gas
pressure switch must therefore be carried out when the burner
is started up, in accordance with the pressure that is found at
the time. The triggering (i.e. the opening of the circuit) of any
of the pressure switches when the burner is running (flame on)
cause the burner to stop immediately. On first switching on of
the burner it is essential to check the correct working of the
pressure switch.
16) Check the triggering of the flame detector (ionisation electro
-
de) by disconnecting the jumper between terminals 30 and 31
on the printed circuit board and switching on the burner. The
equipment must run through its cycle completely and, three
seconds after the ignition flame has formed, “lock-out”. This
check must also be carried out the burner already on. Discon
-
necting the 30 and 31 jumper, the equipment must immedia
-
tely go into its “lock-out” action.
17) Check the proper working of the boiler thermostats or pressu
-
re switches (when triggered they must stop the burner).
IMPORTANT
. Check that the switch on occurs normally since if
the adjuster is shifted forward, it may happen that
the speed of the delivery air is so high that ignition
is difficult. If this happens, the adjust must be shif
-
ted back by degrees until it is in a position in which
ignition occurs normally, and this new position can
be regarded as the final position. We remind you
that is preferable, in the case of the small flame, to
limit the quantity of air to the least possible needed
for safe ignition, even in the most difficult circum
-
stances.
IONISATION CURRENT MEASUREMENT
To measure the ionisation current, remove the jumper
between terminals 30-31 on the printed circuit with the
burner off (see diagram). Connect a microampmeter to the
terminals (with a suitable scale to have the burner restart).
Once the flame has appeared it will be possible to measure
the ionisation current, the minimum value of which to ensure
the working of the equipment is shown in the specific wiring
diagram. After making the measurement, reset the jumper
that has been disconnected.
