Nest cooling instead of heating

[Socalgirl415]

I’ve had my thermostat for a while and have used it for cooling only. Today I decided to test the heat and it’s blowing cold air and dropping the temperature. Please help! 

[Socalgirl415]

 my original wiring 

[Socalgirl415]

 My current wiring. I have tried switching the heat pump from O to B and they both cool 

[zoeuvre]

Hi Socalgirl415, 

Oh no! Sorry to hear that — let me take a look at this for you. 

Turn off the power to your thermostat, and instead of connecting the blue wire to the OB terminal of your Nest Learning Thermostat, connect it to the C terminal instead. Update your thermostat wires on the thermostat itself, then check again if heating will work.

Let us know how it goes.

Best,

Zoe 

[Socalgirl415]

That didn’t work. It gave me an E78 error

[Jenelyn_O]

Hi folks,

@Socalgirl415, thanks for keeping us in the loop. Please provide your Nest Thermostat's power readings under technical Info. Also, please check your system's power. 

First, make sure the power to your system is on. The power switch will usually be in your breaker box or fuse box, but in some homes it will look like a light switch near the heating or cooling equipment. 

1. There may be a single switch, or two switches: one for heating and one for cooling. Make sure the power is on for both then check your thermostat.
2. After you check the power, go to your thermostat and check if it's working.

Next, check that your system's wires are in the right connectors.

1. Pull off the thermostat display.
2. Check that the wires are inserted correctly in the thermostat.

• Check that each wire is fully inserted into its connector and that every connector with a wire is down as shown.
• Check that each wire has ⅜ inch (6mm) of exposed wire.
• Check that each wire is connected properly to the system board.

I appreciate the input, Zoe.
 

Kind regards,

Jenelyn

[Socalgirl415]

It’s shows no power when I switch the blue wire to the C slot from the O/B slot. I can’t get the heater to work on the thermostat but if I switch to my old thermostat the heater works fine. 

[Socalgirl415]

 

[Jenelyn_O]

Hi there Socalgirl415,

Thanks for providing the additional information above. To confirm, did you get that power readings after you switched the blue wire from OB to C? If yes, try to switch back your thermostat wiring from its original configuration then gather the power readings to compare. Also, please share with us the photo of the wires connected to your system's control board. Ensure that the labels of the wires are visible.

Best regards,

Jenelyn

[Socalgirl415]

Yes I got that error after switching from the O/B over to the C. I will upload photos of the wires and power settings now. 

[Socalgirl415]

 

 

[Jenelyn_O]

Hey Socalgirl415,

Thanks for providing the photos above. It turns out that your blue wire isn't the C wire, but a wire for the heat pump. Checking your Nest Thermostat's Energy History would tell us what your thermostat is doing previously. 

Please keep me posted.

Regards,

Jenelyn

[Socalgirl415]

When I try to use the heater it just blows cold air. I can’t get warm air to come from the heater. 

[Socalgirl415]

 

[Jenelyn_O]

Hello there Socalgirl415,

Thanks for keeping me in the loop. To confirm, in what country are you located? Please take a photo of the wires connected to your system's control board. It will help us to ensure the wiring configuration of your system. Also, what is the make and model of your system? 

Kind regards,

Jenelyn

[Socalgirl415]

I’m located in the US. 

[Socalgirl415]

 

[Socalgirl415]

 

[Markjosephp]

Hey folks,

I'm dropping by to ensure everything is covered here.

Thanks for looking into this, Jenelyn.

@Socalgirl415, we appreciate the added details. Looking through the conversation, it appears you have configured your thermostat with a heat pump system. With this, please move the blue wire to the C terminal and leave the white wire at the W1 terminal to avoid the wiring report. Once the wire has been changed, make sure to restart your thermostat to correct its configuration.

Note: Turn off the power from your HVAC system at the breaker box before touching a wire.

Let us know how it goes.

Best regards,
Mark

[Socalgirl415]

Hi mark! I tried that and still receive a no power error. I’ll attach photos. 

[Socalgirl415]

 

[Socalgirl415]

 

[zoeuvre]

Hi all,

@Socalgirl415, chiming in—thanks for getting back to us. After moving the blue wire to C terminal, gather again the Battery, VOC, VIN, and lIN power readouts of your Nest Learning Thermostat under Setting > Technical Info > Power. Also, make sure the thermostat wires are properly stripped and seated in the thermostat base. If the issue still persists, kindly disconnect the C wire then see if the error code no longer shows on the display. 

Thanks for your help here, Jenelyn and Mark. 

Best,

Zoe 

[Socalgirl415]

I switched to my old thermostat and the heater is working fine so it is definitely a wiring issue with the nest thermostat. 

[zoeuvre]

Hi there Socalgirl415, 

Don't give up on us yet—we'd like to further check on this. Could you fill out this form and let me know once you're done?

Thanks,

Zoe 

[Socalgirl415]

form completed 

[Markjosephp]

Hello again,

Thanks for completing the form; we have received it. Soon, a member of our senior support team will contact you via email. So please keep an eye out for any updates and continue the conversation there for any inquiries.

Warm regards,
Mark