The short answer
When a Carrier thermostat in Northern Virginia stops working, it’s usually power, not the thermostat. A blank screen means it isn’t getting 24 volts from the furnace or air handler, or its batteries are dead. A frozen Wi-Fi model can be rebooted by pulling it gently off its wall plate. And codes like E1, E3 and E4 on Carrier’s programmable models each mean something specific. The furnace’s own code light, behind the lower door, often tells you more than the thermostat does.
What you’ll notice
- A blank screen.
- The screen works but the furnace or AC doesn’t respond.
- An E code, or two dashes where the temperature should be.
- The screen freezes or won’t connect to Wi-Fi.
The $67 Heating Check
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A blank screen
Carrier’s thermostats run on 24 volts from the indoor unit, and the Comfort series can also run on two AA batteries when there’s no common wire. So start with the easy ones: fresh batteries if yours takes them, the furnace switch on, the breaker on, and the furnace’s lower door on tight, since the door switch cuts power to the board and the thermostat with it. If the furnace light behind the window is off too, nothing is getting power. If it’s flashing a code, read it in our list of Carrier furnace codes. A code 24 means the 3-amp fuse on the furnace board blew, and that takes the thermostat down with it: see code 24.
What the codes mean
These are from Carrier’s Performance series programmable thermostat manual.
Swipe to see all columns →
Swipe to see all columns →
| What you see | What Carrier’s manual says | What to do |
|---|---|---|
| Two dashes for room temperature | The control can’t read the room temperature, and turns off everything except the fan | Call: the sensor or the control |
| E1 | The display module and the equipment control can’t communicate over their two-wire connection | Call: usually wiring |
| E3 | The control can’t read the outdoor temperature, and shows two dashes there | Call if your system needs the outdoor reading |
| E4 | The control’s internal memory failed | The control gets replaced |
There’s no E2 on that model. An Infinity or communicating control shows its own messages, and our Infinity System Malfunction post covers those.
How to reboot or reset it
- A Carrier Cor or Performance Wi-Fi thermostat: gently pull it off its wall plate and push it back on. Carrier says this reboots it without touching your programming.
- If a reboot doesn’t help, the same models have a reset menu. Reset Preferences puts your schedule and reminders back to default. Reset All goes back to factory settings and clears the registration.
- A Comfort series programmable has a factory reset in its configuration options (Option 99). That wipes the installer settings too, so write them down first, or call us.
When it’s not the thermostat
If the thermostat calls for heat and nothing happens, the problem is usually downstream: a furnace code, a tripped float switch on a clogged condensate line, or a loose wire. Swapping thermostats rarely fixes that. If you’re thinking about a smart thermostat on a Carrier system, our Nest on a Carrier system post covers what works and what doesn’t.
What not to do
Don’t pull the thermostat wires off and touch them together to test the furnace. On some systems that blows the 3-amp fuse, and on a communicating system it can damage the control. Don’t factory reset a thermostat on a heat pump or two-stage system unless you know the installer settings.
What a technician does
We measure the 24 volts at the thermostat and at the furnace board, check the fuse, the transformer and every wire between them, and read the equipment’s codes. Then we fix what’s actually wrong, whether that’s a wire, a fuse, a float switch or the thermostat.
What it costs to have us look
A repair visit starts with a flat $99 diagnostic, and you get the price of the fix before we touch anything. Our Carrier repair page lists what the common repairs cost. Our heating check is $67 per system, through December 31: furnace, heat pump or boiler.
Related: thermostat not working on any system, what thermostat messages mean, the Carrier Edge thermostat, the Carrier Infinity Touch, how to reset a Carrier furnace and the Bryant Evolution version. Other brands are on our error code and warning light guide.
Every code and setting here comes from Carrier’s own documents: Cor and Performance Wi-Fi owner’s manual, Performance programmable instructions and Comfort programmable instructions.
Call or book
Call (703) 997-9757 and tell us the code you counted, or book online from goswiftpro.com/cookiesoffer and a box of warm cookies comes with the visit. Rated 5.0 stars across 1,138 reviews on Google, Angi, Yelp, the BBB and Facebook, Virginia Class A license 2705192276.
Questions people ask
Why is my Carrier thermostat screen blank?
It isn’t getting power. Check the batteries if it takes them, the furnace switch, the breaker and the furnace door. If the furnace’s own light is out too, nothing is getting power.
How do I reset a Carrier thermostat?
On a Cor or Performance Wi-Fi model, gently pull it off the wall plate and push it back on to reboot it. Your programming stays. A full factory reset is in the reset menu.
What does E1 mean on a Carrier thermostat?
The display and the equipment control can’t talk to each other over their two-wire connection. It’s usually a wiring problem.
Does a Carrier thermostat have batteries?
The Comfort series can run on two AA batteries when there’s no common wire. Wi-Fi models run on the system’s 24 volts.
How much does it cost to have a thermostat problem checked?
The visit starts with a flat $99 diagnostic, and you get the price of the repair before any work starts.
