Help with thermostat wiring

[Sporran]

Hi there. 

I have the 6 prong thermostat, but my previous thermostat was using 7 wires, and there is an 8th tucked in that the old thermostat didn’t use. 

I’m confused about the wiring and would appreciate some support. The old one is a trane. 

how it was wired: 

R - red 

W2/x2 - black 

W1 - white 

Y - yellow 

G - green 

O - orange 

B -  blue 

Brown wire not used 

6 wire nest thermostat has: 

y - 

g - 

c - 

w - 

r - 

o/b - 

[David_K · Accepted solution]

Sometimes both the O and B wires are connected at the thermostat but the wires are not actually attached to anything at the other end on the system control board, so it's worth checking that.

Strictly speaking Nest Thermostats are not directly compatible with systems that need both O and B wires. Those wires control when your heat pump cools or heats your home. It is possible to add a relay to resolve this, usually at a zone control panel, in order to make it compatible but for that, I'd recommend consulting professional help. I'll link below guidance on how to do that.

Get installation help or HVAC service from a professional - Google Nest Help