Air Pressure Switch - Viessmann VITOCROSSAL 200 Instructions Manual

Air pressure switch

Function
Fault shutdown
The air pressure switch triggers a fault
shutdown of the burner control unit (see
page 34) 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 volume flow 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 shown with fault
display "L" on the burner control unit (see
page 34 and 39), and cannot be
rectified by pressing the reset button.
The fault shutdown can only be rectified
by shutting down the burner control unit
through switching off the ON/OFF
switch at the control unit.
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.
Before the burner control unit is set to
fault ("L") through a signal from the air
pressure switch, a restart 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
displayed as 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 hygienic combustion.
This will also ensure a minimum pre-
purge, as the air pressure switch still
responds at minimum output.
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