chialex
New Member
Hello experts,
I have a new Navien NCB-240 water heater and I want to install a new Sensi wifi thermostat. That thermostat requires a common wire that would supply 24VAC. On the Navien I found a terminal marked CN25, it has three connectors and in the wiring diagram this terminal is marked as "AC24V, External AC Output". I connected an unused wire the CN25 terminal and the other end to the C connector on the thermostat. I get no voltage on the thermostat through that wire (measured between R and C wires). The other connections I made on the thermostat are R and W, which are connected to the T/T terminal on the Navien. The thermostat works fine with battery backup power, but without the common wire it drops the wifi connection from time to time.
It looks like Navien does have a connection point for the common wire, but I get no current on that connection. Any advice? Could it be that there's a jumper or a switch on the Navien that would supply power to the common wire connection?
I appreciate any insight into this.
Thank you, Alex.
I have a new Navien NCB-240 water heater and I want to install a new Sensi wifi thermostat. That thermostat requires a common wire that would supply 24VAC. On the Navien I found a terminal marked CN25, it has three connectors and in the wiring diagram this terminal is marked as "AC24V, External AC Output". I connected an unused wire the CN25 terminal and the other end to the C connector on the thermostat. I get no voltage on the thermostat through that wire (measured between R and C wires). The other connections I made on the thermostat are R and W, which are connected to the T/T terminal on the Navien. The thermostat works fine with battery backup power, but without the common wire it drops the wifi connection from time to time.
It looks like Navien does have a connection point for the common wire, but I get no current on that connection. Any advice? Could it be that there's a jumper or a switch on the Navien that would supply power to the common wire connection?
I appreciate any insight into this.
Thank you, Alex.
Last edited: