Air Pressure Switch - Viessmann MatriX Service Instructions Manual

Air pressure switch

Function
A
Fault shutdown
The air pressure switch triggers a fault
shutdown of the burner control unit (see
page 22) 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, in control mode, the air pressure
switch fails or the air pressure lies out-
side the permissible range
The fault shutdown is shown with fault
display "L" on the burner control unit (see
page 22 and 29), and cannot be
rectified by pressing reset.
The fault shutdown can only be rectified
by shutting down the burner control unit
through switching OFF the ON/OFF
switch on the control unit.
The signal from air pressure switch A 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 attempt 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 shut-
down through the air pressure switch
("L") will not be displayed as a fault by
the control unit, as it is classified by the
control unit as a maintenance matter
(like a shortage of gas "A").
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.
Air pressure switch
21