Viessmann Vitocrossal 200 Service Instructions Manual page 31

Air pressure switch
Function
Fault shutdown
The air pressure switch triggers a
fault shutdown of the burner control
unit (see page 00) under the following
circumstances:
if the idle state check is not suc-
cessful 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
minimum volume flow is not pro-
duced (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 shown with fault
display "L" on the burner control unit
(see page 00 and 37), and cannot be
rectified by pressing the reset button.
Initial start-up, inspection, maintenance
The air pressure switch A signal is
assessed under the following operat-
ing conditions:
prior to the fan start (idle state
check)
in the pre purge phase
in control mode, as far as at least a
starting output is produced. Outputs
which are lower than the starting
output are not monitored.
The fault shutdown can only be recti-
fied by shutting down the burner con-
trol unit through switching off the ON/
OFF switch at the control unit.
Before the burner control unit is set to
fault ("L") through a signal from the air
pressure switch, a re start will be
initiated 5 times every 2 hours. If
these attempts are unsuccessful, the
burner control unit will be set to fault
("L"). This indicates a serious fault.
The fault shutdown through the air
pressure switch ("L") will not be dis-
played as fault by the control unit, as
it is (like a shortage of gas "A") classi-
fied by the control unit as a mainte-
nance matter.
The air pressure switch is always
set to 1.0 mbar. This guarantees
hygienic combustion. This will also
ensure a minimum pre purge, as the
air pressure switch still responds at
minimum output.
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