Blank screen or dead display
Start with the batteries, since many thermostats run on two AA or AAA cells. If fresh batteries don’t bring it back, the thermostat may have lost its low-voltage power. A common cause here is the safety switch in the AC drain line: when the line clogs, the switch cuts power to the system, and the thermostat goes dark with it. A blown fuse on the control board or a loose wire does the same thing. We find which one it is instead of replacing the thermostat on a guess.
The thermostat says one temperature and the house feels another
Where the thermostat sits matters. One in direct afternoon sun, next to a kitchen, or in the path of a supply vent will read wrong. Dust, a loose wire or an aging sensor can do it too. Put a separate thermometer next to it for a few minutes. If the two disagree by several degrees, call us: we’ll tell you whether it needs a new location, a repair or a replacement.
The AC or heat doesn’t start when you change the setting
Check the basics first: the mode is on Cool or Heat, the setting is past the room temperature, the fan is on AUTO and the batteries are fresh. If that’s all right, the cause is a wire that has come loose, a thermostat that has failed, or a problem in the system itself. We test the thermostat first. If it’s sending the call for cooling or heat and nothing happens, we move on to the system and tell you what we find.
The system won’t shut off
Set the thermostat to OFF. If the equipment stops, the thermostat or its wiring was the cause. If it keeps running with the thermostat off, turn the system off at its breaker and call us. A stuck relay or a shorted wire can keep a system running, and a coil that freezes up from running nonstop is a bigger repair.
Problems that started after a new thermostat went in
A thermostat has to be set up for the system it controls. A heat pump needs extra wiring for the reversing valve, and the wrong setup can make it cool when it should heat. Some smart thermostats need a power (“C”) wire the old one didn’t. If your system acted up right after a thermostat was changed, tell us when you call, and we’ll check the wiring and settings against your equipment.
Settings or schedule keep resetting
Low batteries and power blips are the usual reasons, and so is a smart thermostat that lost its Wi‑Fi connection. We check the power to the thermostat and the wiring, then walk you through the schedule and settings once it’s working.
Smart thermostat won’t connect or respond
A new router, a changed Wi‑Fi password or a weak signal at the thermostat’s spot breaks the link. If the display works but the app doesn’t, that’s usually the connection. If the display is also dead, it’s power or wiring, and we handle that. We can also set up the app and the Wi‑Fi connection for you.
Is the thermostat fine, but the system still not working? That’s a system fault. See AC repair or heating and furnace repair.
Sources: National Weather Service Houston/Galveston, heat and cold stats · U.S. DOE, Energy Saver: thermostats. Checked November 2026.
