Runaway Heat

[captjones]

I installed a Nest gen3 Learning Thermostat 5 days ago. The first night was miserable because the heat kept running though it was saying the AC was cooling. I figured out in the morning that I needed to configure the OB connector for B. I set the thermostat to heat below 68F and cool above 72F. All was well for 4 days/nights.

Last night the heat kicked on while we were asleep and didn't stop. The thermostat read 76F and it was still heating when my wife groggily killed the power to the heating unit about midnight. We woke up this morning and it was 62F. Outside temp was 30F.  I turned the power back on and the heating unit turned on and started warming the house. I expected it to turn off at 68F but it kept heating until it stopped at 74F, then the system switched to AC cooling and cooled the house back down to 71F where it stopped completely and is sitting comfortably now. Outside temp is 45F.

Is there some setting I am missing? Safety temperatures is set to the defaults (40F heat and Off cooling).

Wiring

[Houptee · Accepted solution]

Post pic of old Tstat before you removed it.

Is this a Heat Pump system and do you have electric coil Aux heat?

Or is this gas furnace heat with AC system?

I ask because normally the White wire is for the heat and goes to W1

Orange is normally used for Heat Pumps and go to OB.

So please confirm that you have either a Heat Pump AC system or do yo have a Gas Furnace AC system.

Thanks

[captjones]

Thank you for your quick reply!  We have a Gas Furnace AC system. Original thermostat:

original

[captjones]

Crap! After looking at the pic closer, I see I used the outside labels and not the inside labels! White indeed goes to W and not OB.

[Jenelyn_O]

Hi there,

I saw your post and wanted to chime in — I'm sorry for the delay. I just want to follow up if you're still encountering the issue. Please let me know as I'll be willing to assist you from here. 

Best,

Jenelyn

[Jenelyn_O]

Hi there,

I wanted to follow up and see if you still need help. Please let me know if you’re still having any concerns or questions from here, as I would be happy to take a closer look and assist you further.

Best,

Jenelyn

[Jenelyn_O]

Hi there,

I'm just checking in to make sure that you've seen our response. Please let us know if you have any other questions or concerns as I will be locking this thread in 24 hours.

Best,

Jenelyn

[BryanJBowen]

System was heating & cooling fine for months. Yesterday temp was set to 71 heat & 75 cool. The heater kept running & temp was 86 in the house. I turned unit off & called HVAC maintenance they said everything was connected properly and air conditioner will not engage when outside temp is cold though the thermostat should have cut off the heat. I have a standard 5 tone HVAC all in one unit electric. Another issue which happens when Wi-Fi power was off it lost connection & didn't reconnect. I reconnected it this morning. When Google nest is placed in heat cool mode heater turns back on. Currently have thermostat set to heat only mode heater is turned off at set temp. Software 6.2-27 no update available. I'm thinking when you make a patch for this software version it will resolve the issue.

[aslwinlam]

similar issue with mine. my heat setting was 66 outside temp was 68. The heater turned on and run up to 71..looking at history .the unit ran each day to 71 but the setting was at 66..