Viessmann Vitocrossal 200 CM2 500 Service Instructions Manual page 33

Vitocrossal 200, CM2 400, 500 and 620 Service
Further Details Regarding the Individual Steps
Combustion chamber pressure monitoring
(air pressure switch 2)
To monitor the combustion chamber pressure, the
switching threshold of air pressure switch 2 is monitored
in all operating phases (except safety and stabilizing times).
Air pressure switch C triggers a fault shutdown of the
burner control unit under the following circumstances:
■ If the combustion chamber pressure is outside the
permissible range in the pre-purge phase, in control
mode or in the post-purge phase after 2 attempts.
The fault shutdown is shown with fault display "F Fb"
on the burner control unit (see page 49) and can be
rectified by pressing reset button R B.
Boiler model Air Pressure Switch 2 Adjustment Value
in mbar
400
500
620
Air pressure switch setting example shown
5
(continued)
Gas inlet pressure monitoring switch - GDW1
The factory default setting for the gas inlet pressure switch
is 10 mbar (4" w.c.). This is the minimum gas pressure
required for the burner to operate with natural gas fuel.
For liquid propane gas the switch can be left at factory
default setting of 10 mbar (4" w.c.) or increased to
22.4 mbar (9" w.c.). This setting can be changed by
removing the GDW1 cover and manually setting the dial.
The inlet gas switch GDW1 will trigger a stand still (waiting)
state of the burner control unit when the gas pressure drops
below the setpoint. The burner will retry after 5 minutes if
the gas pressure returns to the setpoint threshold.
Valve seat gas pressure monitoring switch - GDW2
(outlet pressure at first valve seat)
The factory default setting for valve seat gas pressure switch
is 10 mbar (4" w.c.).
The switch will trigger an E1 (pressure) or E2 (open circuit
during control self diagnostics) faults on the burner control,
if activated.
IMPORTANT
Do not adjust this switch.
Legend
A GDW1 - gas inlet pressure monitoring switch
B GDW2 - valve seat gas pressure monitoring switch
Burner Service
33