2126
11
GB
BURNER STARTING DIFFICULTIES AND THEIR CAUSES
UV CELL CURRENT
Minimum value for correct operation: 15 µA. A lower
value can be due to: spent cell; low voltage
(lower than
207V)
; inaccurate burner adjustment. To measure the
value, use a 10 µA c.c. microammeter connected in
series to the cell, as shown on the right, with a 100 µF
– 10 V c.c. condenser in parallel with the instrument.
Valid for GAS operation; valid also for LIGHT OIL operation when marked (
)
DIFFICULTIES
CAUSES
The burner goes through
pre-purging normally and
the flame ignites but it
stops within 3 seconds from
ignition.
UV cell not working: dirty, spent, low voltage (lower than 207 V).
(
)
The gas pressure switch is calibrated to a value too near the oper-
ating pressure.
The flame does not ignite
and the burner stops after (or
during) pre-purging.
Not enough gas through valve.
Faulty or no ignition electric arc.
(
)
Air in the pipe.
The air pressure switch does not close the contact: mal-adjusted or
faulty; continuous pre-purging.
(
)
The burner does not start
when the thermostat closes.
No gas.
The air pressure switch does not close the contact: mal-adjusted or
faulty.
The burner goes on repeat-
ing the starting cycle without
any lock-out.
It is a particular malfunction due to the gas pressure being very
near the value of the pressure switch.
The sudden drop in pressure when the valves open causes the
pressure switch to open temporarily and, as a consequence, the
valves close again and the motor stops.
Pressure then increases, the pressure switch closes and the
starting cycle begins again, and so on.
The burner can sometimes go into lock-out for the same reason.
Lowering the pressure setting of the switch can solve the problem.
UV cell
+
+
–
–
D5841
8
Control box
