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Wiring Diagram
Additional Information
PCB1 Mother circuit board
PCB2 Diode circuit board
F
Fuse
K1, K2,
K4
Relays
S1
DIP switch
S2
Power switch
S3
Space heating switch
AHL
Adjustable high limit
FHL
Fixed high limit
PA
Pump aquastat
120 VAC Connections
Power supply (120 V, 60 Hz)
Heating circuit pump
Burner connection
ALT
Alternative input/output
TEST FHL test terminal
24 VAC Connections
X2 Room thermostat connection or
DHW pump module connection
191
2nd stage cable connection
This wiring diagram applies only to
installations where Viessmann products
are used.
Technical information subject to
change without notice.
Wire color code
BK black
BN brown
RD red
OG orange
GN green
BU blue
VT violet (purple)
GY gray
WH white
*The terminal designation shown will
depend on the switch model used.
25
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