Air Pressure Switch - Viessmann VITOCROSSAL 200 Service Instructions Manual

Air pressure switch

Function
Fault shutdown
The air pressure switch triggers a fault
shutdown of the burner control unit (see
page 33) under the following circum-
stances:
■ 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, during the control mode, the air
pressure switch fails or the air pres-
sure lies outside the permissible range
The fault shutdown is indicated with fault
display "L" on the burner control unit (see
page 33 and 38) and cannot be rec-
tified by pressing the reset button.
The fault shutdown can only be rectified
by shutting down the burner control unit
by switching off the ON/OFF switch at
the control unit.
32
The air pressure switch A signal will be
interpreted 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. Any
output lower than the starting output is
not monitored.
A restart will be initiated 5 times every 2
hours before the burner control unit is set
to fault ("L") through a signal from the air
pressure switch. The burner control unit
will be set to fault ("L") if these attempts
are unsuccessful. This indicates a seri-
ous fault. The fault shutdown through the
air pressure switch ("L") will not be dis-
played as a fault by the control unit, as
it is (like a shortage of gas "A") classified
by the control unit as a maintenance
matter.
At 87 kW, the air pressure switch is
always set to 0.8 mbar (minimum) and
at 115 to 311 kW to 1.0 mbar.
This guarantees clean combustion. This
will also ensure a minimum pre-purge, as
the air pressure switch still responds at
minimum output.