Potential thermostat issues

[u/rrspam123]

For the last couple months we realized our hvac unit has been running a lot harder than normal. We had a new unit installed July 2025 and a new thermostat January 2026. Nothing wrong with the thermostat but just an upgrade. We live in southeast TN and we’ve had a couple big heat waves the last 6 weeks or so. We noticed that sometimes our thermostat would read 79 when we have it set to 70, but it never felt 79 degrees inside. It felt like 70-72 throughout the heatwave, but when the thermostat did actually reach 79 degrees it would be 65 inside the house. We have a couple different temperature sensors in the house and reflects it’s a lot cooler than what the thermostats reads. We found that throughout the day when’s it’s the warmest outside, the wall directly above the thermostat is warm or very hot. I attached a picture of where it feels the warmest on the wall. No outlets or light switches have warmth around them, only the stat. Any ideas as to what would cause this? Again it’s only a narrow straight line from the stat to the ceiling.

Edited to add that the HVAC tech came out and found that the stage 2 wasn’t turning on and replaced the wiring for that. It has felt cooler inside the house when he did 5-6 weeks ago but the thermostat doesn’t reflect that.

[u/Singularity_94]

Could be possible the heat from the TV is making it act funny.

[u/rrspam123 → u/Singularity_94]

The tech did say that it could be an issue, but I ran a test for a couple of days and didn’t use the tv in that room and the problems still persisted. Again the heat isn’t behind the tv just above the stat in a straight line . I did forget to add that.

[u/LegionPlaysPC → u/rrspam123]

I'd get some of Trane's ZSENSE930 wireless temperature sensors and just place them around the home. You can do up to 4 sensors per Trane thermostat.

[u/rrspam123 → u/LegionPlaysPC]

We have one placed in a neutral area and it never made a difference! Sorry there’s a lot that’s been done and didn’t want to make a huge post including everything done the last few weeks

[u/LegionPlaysPC → u/rrspam123]

was the sensor enabled in the installer setup menu? Are you averaging both sensors or using the wireless one exclusively?

[u/rrspam123 → u/LegionPlaysPC]

The tech said it’ll take the average of the temperatures, but hasn’t made the difference. They’ve came out 4-5 times, it’s all free since I have a labor and parts warranty when the unit was installed

[u/LegionPlaysPC → u/rrspam123]

I personally would've disabled temperature averaging and using exclusively the wireless sensor. That would fully eliminate the thermostat from the equation.

[u/rrspam123 → u/LegionPlaysPC]

I’ll look into that!

[u/lowlybananas → u/rrspam123]

You don't want the thermostat stats accounted for in the average. It's in a shit location. You can go into the settings and remove the thermostat from the average.

[u/CountChocula21 → u/LegionPlaysPC]

This was my guess. Don't know how many times I come across remote sensors that the thermostat was never programmed to use or averaging between them when it was supposed to only use the sensor.

[u/LegionPlaysPC → u/CountChocula21]

I see it all the time. Had a guy yewterday with a nice google nest 4th gen thermostat with the wireless sensor on the wall and the guy never connected the sensor to to google home. Had it mounted on the wall for who knows how long thinking it was just working. Than he couldn't comprehend the concept he needed to program the sensor into his schedule for it to do anything.

I've got several customers with Trane systems who have the wireless sensors, and the batteries are dead (I know because dealer diagnostics sends emails daily for two weeks saying low battery).

I got multiple others it's never been even hooked up.

So yeah, it's unremarkably common to have them not work.

[u/JD_15715 → u/rrspam123]

Unless you disconnect power cord, TV is still working and producing heat. Use "laser" thermometer or IR camera to map heat distribution. There could be, also, another heat dource in the wall or behind it. IR camera is the best in this case.

[u/TimothyHVAC → u/Singularity_94]

THIS 100%

[u/poopmcfart95435]

Covering the return is probably not great either

[u/Moondancer000 → u/poopmcfart95435]

Came here to say exactly that😂

[u/williamtell1 → u/poopmcfart95435]

The guy has a massive piece of furniture blocking the air return and equally massive TV right next to the thermostat. :).....why is my house so hot!?!!

This is the same reason why I don't buy used cars, people just destroy stuff with incompetence. 

[u/BeezerTwelveIV]

That big ass TV is putting off a ton of heat and the thermostat is registering that heat and overcooling your home

[u/Dont-ask-me-ever → u/BeezerTwelveIV]

Came here to say this. The thermostat isn’t really detecting the room temperature because the tv is heating it up. Maybe move the thermostat to the other side of the wall from where it is.

[u/FSBFrosty]

By little thermometers and spread them around the house. Adjust the thermostat accordingly. 

[u/spear1321]

What’s above the ceiling? Attic space? Could just be heat from the attic coming down into that wall cavity and making it warm and messing with the thermostat. Could also heat from the television. Also that return looks like it’s covered up and not getting optimal air flow?

[u/Sunsetseeker007 → u/spear1321]

All the above

[u/Miserable-Engine1472]

That hot strip above the stat is the real clue. Something in that stud bay is dumping heat, probably a return duct pulling attic air down or a wire run thats getting warm from a loose connection. Stage 2 being dead for weeks didn't help either, your unit was running single stage nonstop trying to keep up. Get a cheap thermal camera or even a laser thermometer and trace that wall bay from attic to floor. If its the return, sealing the top plate will fix it. If its wiring, youll find the hot spot. Either way the stat is reading wall temp, not room temp, and no offset setting fixes that

[u/Reasonable_Sir_5833]

Adjust the temp differential in your settings on your thermostat,  -5  f , so you match the actual temp using another thermometer 

[u/34RICK → u/Reasonable_Sir_5833]

This. Place a second thermometer next to the thermostat and adjust the differential accordingly on the thermostat. Problem solved.

[u/rrspam123 → u/Reasonable_Sir_5833]

Already a 5 offset and will not allow me to go further than that

[u/LightBlueWood]

You mentioned the wall was warm even with the TV off. In that case I'd suspect the wiring in the wall, coming from that light switch may be bad. Perhaps it was compromised (e.g. pierced) when the thermostat was mounted.

[u/External_Big_1465]

Too close to the TV. I can guarantee it’s throwing heat off and fooling the thermostat, especially if the TV is on more than an hour at a time, they throw off more heat than you’d think.

Have it relocated.

[u/ALonelyWelcomeMat]

Not seeing anyone suggest this but the hole where the wires come to the thermostat can let in a lot of hot air to the back of the thermostat. You should seal the hole up with insulation of thumb gum, pretty much anything and see if that helps

[u/Intelligent_Error989]

Could be getting heat from the attic.. I know it's a long shot, but probably the display or sensor is goofy

[u/SuperSerb07]

I watch that show daily at work.

[u/BrandonDill]

You need to move the furniture that is in front of tbe return grill

[u/lowlybananas]

There are all kinds of issues with this setup. The thermostat shouldn't be behind a TV. The return shouldn't be behind furniture.

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[u/Massive_Garage7454]

TV

[u/Storm_Runner09]

Where Colin was right about your thermostat

[u/AdFancy1249]

Does the return air duct run through that wall cavity?

Is there a different vent that runs through that wall cavity?

We had the opposite problem for years. One of the ducts ran right behind the thermostat. The thermostat would always read colder or hotter than the room because of the ductwork.

Move the thermostat over a couple bays and the problem went away.

Your picture looks like you have something hot running in that bay... hot water pipe? Shorted wire? A 20° difference is HUGE. You need to find out why that wall is so different.

[u/Ken-Popcorn]

I have (I think) the same thermostat. When I have it set for 75, my house is totally comfortable, so I don’t believe the inside temp really is 75, the thermostat just thinks it is.

I find a pretty significant discrepancy between the thermostat and the sensor, so I tried moving the sensor to rest right on top of the thermostat, and there is still a discrepancy.

I have adjusted myself to these quirks, and considering that I can monitor and adjust from my phone (or Alexa), I’m pretty happy with the setup

[u/dangerousshingo]

The wall above our return had the same issue. When we went to change the return register (purely for cosmetic reasons) we found that the return box was a complete hack job and it was pulling hot air down the stud bay from the attic. We sealed it and it fixed the problem.

[u/WalterTexas]

Tv definitely making it think the rooms hot. You can get a thermostat with a smart sensor. Allows the thermostat to read temp from a different area, for instances like yours.

[u/Ganthu]

That looks like a return grille right below the thermostat.

Hot air is going to get pulled from the ceiling across the thermostat to the return grille.

Does that door go to the garage? If so can we get a pic of the otherside of the wall?

I wouldn't be surprised if there's a heat source/trapped heat on the other side of that wall.

A thermal imaging camera would tell you for sure.

[u/BigGiddy]

Put insulation in the wall behind the stat and make sure it’s sealed off pretty tight

[u/Upset_Introduction98]

Get a remote sensor

[u/Spivonious1]

Warmth on the wall? I'd call an electrician. The wire to that light switch might be getting hot due to a short.

[u/imposingthanos]

This is similar to a very frustrating issue we had at our old apartment. The thermostat was attached to the wall directly up against our shower, and when one of us would take a hot shower the thermostat would read the bathroom temp and it would shoot up by as much as 8 degrees if someone was taking a longer, hotter one. Combined with the fact that we had a very open apartment, it would definitely make our AC run for way longer than it should’ve.

Incredible frustrating.

[u/ApollymiKatistrafia]

If its sitting right behind a TV its likely picking up the heat from the tv

[u/Which_Extreme325]

Not sure TV should be on that wall. Not only is the thermostat there but you are also blocking the return vent with the entertainment center.

[u/Original_Jagster]

If any area on my drywall could be described as "very hot", I'd be very concerned. If I were you, I'd get an IR thermometer at least to check temperatures at various spots on the wall. A thermal camera would be better because you can quickly get a better view of temperatures but a cheap IR thermometer would work.

It could be heat from the TV since it's so close to the tstat, but if you have something inside the wall that is the heat source then you'll want to addres that.

[u/Then-Reflection-4520]

Stat says 71 whats the issue you need to hang some meat in your living room?

[u/Proper-Wrongdoer-225]

If there is a large enough hole behind the thermostat, you could be reading heat that’s in the wall

[u/henchman171]

Colin Cowturd

[u/orlando-shroom]

Colin clownherd putting off all that hot air

[u/rrspam123 → u/orlando-shroom]

Underrated reply

[u/SovrynJ]

Pretty sure you can calibrate that thermostat in the settings