Navien NFB-175H, Installation Manual, Page: 41 / 135

41 Installing the System Piping
3.6.5 Wiring Diagram - Zone Valve System
The NFB-H Boilers can operate a heating system with up to 3 zones. The following is the wiring diagram for a zone
valve system with 3 zones.
Without 24VAC connections
COM
A/
H
DHW
PRI
NO
NC
N
L
N
L
N
L
COM
NO
NC
ZONE1
COM
NO
NC
ZONE2
COM
NO
NC
ZONE3
AC24VN
SUPPLY RETURN OUTDOOR DHW TANK
AC24VL
LWCO
R
W
C
R
W
C
R
W
C
R
W
C
System pump
(max. 2.5 A)
COM
A/H
DHW
PRI
NO
NC
N
L
N
L
N
L
DHW pump
(max. 2.5 A)
Boiler pump
(max. 2.5 A)
Pump Ground
NC
NC
COM
NC
NC
COM
LWCO
AC24VL
AC24VN
NC
NC
COM
ZONE1
ZONE2
ZONE3
COM
NC
NC
ZONE1
COM
NC
NC
ZONE2
COM
NC
NC
ZONE3
AC24VN
SUPPLY RETURN OUTDOOR DHW TANK
AC24VL
LWCO
R
W
C
R
W
C
R
W
C
R
W
C
Thermostat 1
Thermostat Input
24 VAC L
DHW Aquastat
(priority)
Thermostat 2
Thermostat Input
24 VAC L
Thermostat 3
Thermostat Input
24 VAC L
NC
NC
COM
NC
NC
COM
LWCO
AC24VL
AC24VN
NC
NC
COM
ZONE1
ZONE2
ZONE3
COM
NO
NC
ZONE1
COM
NO
NC
ZONE2
COM
NO
NC
ZONE3
AC24VN
SUPPLY RETURN OUTDOOR DHW TANK
AC24VL
LWCO
R
W
C
R
W
C
R
W
C
R
W
C
Zone valve 1
(max. 1A)
Zone valve 2
(max. 1A)
Zone valve 3
(max. 1A)
Note
●
NO (Normal Open): Power is supplied when the zone valve is operating, and power turns off when
the zone valve stops.
●
NC (Normal Close): Power is supplied when the zone valve stops, and power turns off when the
zone valve is operating.
●
COM: 24 V AC COMMON
●
The boiler has an internal 24V transformer that is rated for 75VA. This transformer provides power
to the zone valve, low water cut-off (LWCO) and thermostat terminals.
●
If the total power consumption of all 3 zone valves exceeds 70VA, an external zone valve controller
must be used.