26
Function
A
Fig. 23
The signal of air pressure switch
A
is evaluated in the
following operating situations:
■
Prior to the fan start (idle state check)
■
In the pre-purge phase
■
In control mode, subject to the output being no lower
than the starting output. Any output lower than the
starting output is not monitored.
Fault shutdown
The air pressure switch triggers a fault shutdown of the
burner control unit under the following circumstances:
■
The static pressure check has remained unsuccess-
ful after 5 attempts (anti-cycling function). This
means the air pressure switch contact did not open
within 30 s.
■
The minimum flow rate was not conveyed during the
pre-purge phase (fault shutdown via the anti-cycling
function).
■
The air pressure switch fails in control mode or the
air pressure lies outside the permissible range.
The fault shutdown is indicated with fault codes "F AA"
and "F AB" on the burner control unit display. To
acknowledge the fault display, press the reset button
(min.
¼
s).
This indicates a serious fault. The fault shutdown by
the air pressure switch is displayed as a fault in the
control unit
.
The air pressure switch is set at the factory.
The default setting made at the factory ensures
hygienic combustion. A minimum degree of pre-purg-
ing is ensured, as the air pressure switch still responds
at minimum output.
Burner control unit
Display and programming unit
Function
A display and programming unit is integrated into the
burner control unit. The display screen shows the rele-
vant operating status, the service and parameter sta-
tus, as well as any fault or error messages.
Air pressure switch
5783 337 GB
Diagnosis
