Will not heat above certain temperature

[khadotcom]

We have the heater set at 73 degrees but the furnace won't go above 71.  I don't have a common C wire.  

[CoolingWizard]

The Common wire has nothing to do with the temperature setpoint. When the temperature does not get above 71°F, is the system continuing to run and not getting warmer or does it stop at 71° and turn off?

Ken

[khadotcom]

The system stops running.  It never goes over 71 degrees. 

[CoolingWizard]

If set the heat to 78,,does it still stop at 71?

Ken

[fcclp01]

Yes, for me aksoy

[EdwardT]

Hi folks,

@CoolingWizard, thanks for the help!

@fcclp01, I wanted to follow up and see if you are still in need of any help. Please let me know if you are still having any trouble from here, as I would be happy to take a closer look and assist you further.

Thanks,

Edward

[fcclp01]

Yes,  I am still having that issue...not going above 71  degrees

[khadotcom]

Yes...it will stop at 71.  This is only when when the temperature outside is in the 40s and 50s.  Midday or afternoon, it can go up to 74 when I set it to 75.  However, I don't know if it is the furnace that is bringing it up to 74 or just the day getting hotter.  We are in Los Angeles area.  It seems like the power cuts off when it is cold outside.  Can it be the furnace temp sensor? 

[CoolingWizard]

Well, you’ve given a couple situations here that one could be the thermostat itself the other could be the problems in the heating system. Basically, the reason I asked is if you set the temperature higher I’m trying to see if there’s a 2° error or if there’s a problem with the heating system. it does not matter what the outdoor temperature is because the thermostat is indoors. What does matter is where the heater is located and how it reacts to the exterior temperature. For example, if you have a heat pump, it’s its performance is outdoor temperature related. But it hasn’t been cold enough in Los Angeles to cause a problem. I’m a few hours south of you in Imperial County California. 

[EdwardT]

Hi folks,

@CoolingWizard, thanks for the help!

@khadotcom, how's it going with your Nest Thermostat? Still need our help?

Thanks,

Edward

[EdwardT]

Hi khadotcom, 

It's me again. I wanted to check back in to see if you have other questions and concerns. Feel free to let me know if you do. 

Thanks,

Edward

[EdwardT]

Hi khadotcom, 

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 in 24 hours.

Thanks,

Edward

[fcclp01]

I am having the exact same problem. My thermostat will not go above 71°. Even if I said it at 78°.

[EdwardT]

Hi fcclp01,

Thanks for letting us know. Is it doing the same thing where the system stops running when it hits 71°?

Thanks,

Edward

[fcclp01]

Yes it is doing the same thing

[CoolingWizard]

If you have hydronic heat, sometime the system and not the thermostat can be the problem.  Have found defective hydronic thermistors on the boiler and radiators.  Just take a moment and test them.  

Ken

[fcclp01]

No, I do not have hydronic heat.

[EdwardT]

Hi fcclp01,

Thanks for the response. I'd love to know more about this and I have a few questions:

• What type of Nest Thermostat do you have?
• How is your Nest Thermostat wired?
• What is the power reading of your Nest Thermostat? You can find this information by going to Settings > Technical Info > Power.

Looking forward to your response.

Thanks,

Edward

[fcclp01]

My NEST is Display 4.9.

backplate mode 7.6

serial no 15AA01AF202002MP

Device id 6416660000F5151A

I do not see the other information you are looking for.

[EdwardT]

Hi fcclp01,

Thanks for the response. We'd like to know more about this. Please fill out this form so we could investigate further.

Thanks,

Edward

[EdwardT]

Hi fcclp01,

I'm checking back in. Were you able to fill out the form? Let us know if you have questions and we'd be glad to assist you.

Thanks,

Edward

[EdwardT]

Hey fcclp01,

I wanted to follow up and see if you are still in need of any help. Please let me know if you are still having any trouble from here, as I would be happy to take a closer look and assist you further.

Thanks,

Edward

[khadotcom]

Hi,

Sorry I was on vacation for a week and just got back.  Currently, the Nest is working normally.  The outside temperature has been warmer so it has no difficulty with reaching the desired temperature.  My guess is that if the system is working too hard or running too much to get to 76 degrees, then Nest will settle for 71 or 72 and try to maintain it there even if I put 76.  I will wait for another cold spell here to see if it is the case. 

[Jake]

Hey there,

Thanks for the helpful reply Ken.

I wanted to check in and see if you managed to see Ken's post. Please let me know if you have any questions from here. I would be happy to assist, and make sure you are good to go.

Best regards,
Jake

[Jhonleanmel]

Hi folks,

Chiming in to see if you still need assistance with this. Let us know if you have additional questions ― we'd love to help.

Best,
Mel

[Jhonleanmel]

Hi everyone,

Just one quick final check in here since activity has slowed down. We haven't heard from you in a while so we'll be locking this thread if there is no update after 24 hours. If you have any new questions, updates or just a discussion topic, feel free to start a new thread in the Community.

Thanks,
Mel

[CoolingWizard]

When I see systems that are acting this way, I tend to find that the problem is mostly related to the heating system itself. For example, if you have a combination, forced air heater with an air conditioning evaporator coil on top, and that air conditioner coil is not clean, it limits the air’s ability to go through and heat the home. Sometimes it also can be that you have a two-stage heating system it’s only operating at a single stage mode. This is not likely because your old thermostat did not have a two-stage heating system. 

I would like to try to help you more with this, but I believe a telephone conversation is the only way we’re gonna be able to solve this for you.

Ken, The AC Cooling Wizard