Function Description; Air Pressure Switch - Viessmann Vitocrossal CRU 800 Service Instructions For Contractors

Air pressure switch

Fan pressure monitoring function (LDW1)
The switching threshold of air pressure switch 1 (plug
aCA ) is monitored in all fan ramp-up phases and
checked during modulating burner operation. This
ensures a minimum pre-purge.
Air pressure switch 1 triggers a fault shutdown of the
burner control unit under the following circumstances:
■ The static pressure check was unsuccessful after
approx. 5 minutes.
■ The air pressure is outside the permissible range
during the pre-purge phase. Tolerance time approx.
5 min.
The air pressure switch fails in control mode or the
■
air pressure lies outside the permissible range.
Combustion chamber pressure monitoring function (LDW2)
To monitor the combustion chamber pressure, the
switching threshold of air pressure switch 2 (plug
A) is monitored in all operating phases (except dur-
aCA
ing safety and stabilising time).
If the combustion chamber pressure lies outside the
permissible range, air pressure switch 2 triggers a fault
shutdown on the burner control unit.
The combustion chamber pressure lies outside the
permissible range in the following operating phases:
In the pre-purge phase
■
In control mode
■
■ In the post-purge phase after 2 attempts
Boiler water temperature sensors and flue gas temperature sensors
The temperature sensors are of a dual sensor design.
Connection to burner control unit:
B Boiler water temperature sensors
§ A/ §
A/ B Flue gas temperature sensors
aG aG
The fault shutdown is indicated by fault codes "F F5"
and "F F7" on the burner control unit display (see
page 39).
Fault resetting: Hold down reset button R for longer
than 0.5 s.
LDW1 setting:
Rated heating output 800 kW: 2 mbar (0.2 kPa)
■
■ Rated heating output 1000 kW: 4 mbar (0.4 kPa)
The fault shutdown is indicated by fault code "F FB" on
the burner control unit display (see page 39).
Fault resetting: Hold down reset button R for longer
than 0.5 s.
LDW2 setting: 10 mbar (1 kPa)
NTC 10 k
Ω
20
10
8
6
4
2
1
0.8
0.6
0.4
10 30 50
Temperature in °C
Fig. 30

Function description

70 90 110
57