33
Function
A
The air pressure switch
A
signal is
assessed under the following operating
conditions:
■ prior to the fan start (idle state check)
■ in the pre-purge phase
■ in control mode, subject to at least a
starting output being produced. An
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:
■ if the idle state check is not successful
after 5 attempts (anti-cycling function)
(i.e the air pressure switch contact
does not open within 30 s)
■ if, during the pre-purge phase, the min-
imum flow rate is not produced (fault
shutdown via the anti-cycling function)
■ if, in control mode, the air pressure
switch fails or the air pressure lies out-
side the permissible range.
The fault shutdown is indicated with fault
codes "F AA" and"F AB" on the burner
control unit display. This can be rectified
by pressing the reset button (for at least
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.
This guarantees hygienic combustion.
This will also ensure a minimum pre-
purge, as the air pressure switch still
responds at minimum output.
Air pressure switch
5692 908 GB