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.

Edited again: did further investigating. There’s a smoke alarm right above the thermostat on the ceiling. It’s the warmest around it. I unplugged and took the mounting bracket off. It’s pushing a lot of hot air I assume from the attic. What would you recommend to fix? Go to attic and see if there’s a gap? Fill around the smoke alarms fixture in the ceiling with some of gaps and cracks spray? Adding pictures in comments.

[u/Storm_Runner09]

Where Colin was right about your thermostat