Trying to install nest thermostat can’t get O/B wire recognition

[Kir]

We have tried to install two thermostats with two heat pump systems and getting same issue each time

It won’t recognize O/B wire

[zoeuvre]

Hi Kir, 

Oh no! I'm sorry to hear that your thermostat does not recognize your OB wire. A few questions:

1. Are you located in North America or Europe?
2. What type of Nest Thermostat do you have?
3. What is the make and model of your heat pump system?
4. Is there any code or message that appears on the thermostat?

You may also try the following: 

1. Make sure the heat pump system and thermostat have the O/B wire connected correctly.
2. Make sure the thermostat wires are properly stripped and seated in the thermostat base.
   
   • Turn power to your system off at the system switch or fuse box. This helps protect your system and thermostat from possible damage.
   • Pull the thermostat display off the base.
   • Pull out one wire and inspect it.
     • The exposed part of the wire should be ⅓ to ½ inch long, clean and straight
     • Cut and re-strip any crooked or corroded wire ends
   • Re-insert the wire.
   • Make sure that the wire connector’s button stays down. If not, the wire isn’t fully inserted, and the thermostat won’t detect it.
   • Once you've checked all the wires, push the display onto the base until you hear a click.
     Turn power to your system back on.
3. Using a multimeter or voltage tester, test the O/B wire for proper voltage and continuity to identify wiring issues or confirm its correct functioning.
   • Set the dial to 200 VAC.
     • If the multimeter doesn’t have a 200 setting, choose 100 or 250 VAC.
     • The general rule of thumb is don’t set it too high (500+) or too low (50). Place the red lead on the R wire.
   • Place the black lead on the OB wire.
   • The normal readout should be somewhere between 20 and 30 V (24 V is most common).

Keep us posted. We're happy to help.

Best,

Zoe