Wondering what's going on in there?
How your Honeywell works, in plain English
Your Honeywell is a switch with a brain. It doesn't heat or cool anything. It tells your furnace or AC when to run.
- Power. Some Honeywells run on batteries. Wired ones get low power from the furnace, often through a wire the pros call the C-wire. Honeywell says they run on 20 to 30 volts. No power, blank screen.
- The call. When the room is off from your setting, it sends a signal down thin wires. Honeywell says a steady Heat On or Cool On means it's calling.
- The furnace or air handler. It starts only if its power is on, its front panel is shut tight, and its drain isn't backed up. Each has a safety switch.
- Heat or cooling. The furnace heats, or the AC outside starts. Honeywell says many systems wait about 5 minutes after a change, to protect the AC's compressor.
So a thermostat that "isn't working" is usually one of these:
- No power: batteries, a switch, a breaker, the furnace panel, or a backed-up drain.
- A setting: the mode, a schedule, a hold, or the fan.
- The thermostat itself, its wiring, or a missing C-wire.
- The furnace or AC, not the thermostat.
The questions at the top check these in the same order. Thermostat fine, but no heat? See a furnace that won't turn on or a furnace blowing cold air. No cooling? See an AC blowing warm air.
Rather not do it yourself? Call an HVAC tech.
That's a fine choice. Maybe you're busy. Maybe you're selling the house and just want it done right. An HVAC tech (a heating and cooling pro) can fix the wiring or put in a new thermostat.
Most companies charge $75–$250 to come out, and many put that toward the repair.
Find HVAC repair near you
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What to say
Calling a pro? Here's what to say.
A few lines to read when they pick up, and the questions to ask before anyone comes out.
Before you call
Say this
Hi. My Honeywell thermostat isn't working. When's the soonest you can get here? And what's your fee for the visit? Does it go toward the repair?
Always ask
- What's your fee to come out, and does it go toward the repair?
- Will you tell me the full price before you start any work?
- Are you licensed and insured?
Watch out if
- They push a whole new system on the first visit for a small problem.
- They won't give you a price before starting.
- They want to "just add refrigerant" every year without finding the leak.
Feeling pushed to decide on the spot? You can say no and hang up. You owe nothing for a phone call.
Answer up to 5 quick questions. We'll give you the words a pro uses.
Answer the questions →More of a list person?
Common thermostat problems, causes, tests and costs
Find the row that sounds like yours. The quick test is something you can check yourself in a few minutes.
| What you notice | What it probably is | Quick test | Do it yourself | With a pro | Verdict |
|---|---|---|---|---|---|
| Screen blank | The thermostat's batteries are dead | Pop the thermostat off and look for batteries | $0–$10 | Not needed | FIXSee the answer: The thermostat's batteries are dead |
| Furnace switch off, or the furnace or AC breaker tripped | The system's power was off | Look at the furnace switch and the breaker box | Free | Not needed | FIXSee the answer: The system's power was off |
| Furnace front panel loose, crooked or off | The furnace door switch | Press the front panel. Is it seated all the way? | Free | Not needed | FIXSee the answer: The furnace door switch |
| Water in the pan under the indoor unit, or around the furnace | A clogged drain shut the system off | Look for water in the pan under the indoor unit | $0–$30 | $75–$250 | FIXSee the answer: A clogged drain shut the system off |
| Blank; comes back when pushed firmly onto the wall plate | It wasn't seated on the wall plate | Press it firmly onto the wall plate | Free | Not needed | FIXSee the answer: It wasn't seated on the wall plate |
| Works on batteries only; furnace door, switch and breakers fine | Power from the system isn't reaching it | Try it with and without batteries | Pro job | $60–$200 | CALLSee the answer: Power from the system isn't reaching it |
| New thermostat won't power up or run | A setup problem on a new install | Check the C wire and the jumper switch | Free | $80–$200 | FIXSee the answer: A setup problem on a new install |
| Wrong mode, a schedule or hold running | The settings are wrong | Look at the mode, the set temperature and any Hold | Free | Not needed | FIXSee the answer: The settings are wrong |
| Air blows all the time, but it isn't warm or cool | The fan is set to On | Look at the Fan setting | Free | Not needed | FIXSee the answer: The fan is set to On |
| Wait shows, or Heat On or Cool On is flashing | It's in a safety delay | Wait 5 minutes and watch the screen | Free | Not needed | FIXSee the answer: It's in a safety delay |
| Thermostat clicks, but nothing runs; or the house stays off | The furnace or AC has a problem | Set it 5 degrees past the room and wait 5 minutes | Pro job | $50–$150 | CALLSee the answer: The furnace or AC has a problem |
| Blank with fresh batteries and power; or no Heat On or Cool On | The thermostat has failed | Rule out batteries, power and settings first | Pro job | $85–$600 | CALLSee the answer: The thermostat has failed |
| Smart thermostat says "no power" or "C-wire," or keeps going offline | It needs a C-wire | Look for a C-wire message in the thermostat's app or screen | Pro job | $90–$135 | CALLSee the answer: It needs a C-wire |
| Reads warmer or colder than the rest of the house | Something is fooling the thermostat | Look for sun, lamps, vents or drafts near it | Free | Not needed | FIXSee the answer: Something is fooling the thermostat |
| Old round or dial Honeywell; house doesn't match | An old or dusty thermostat | Look at its age and for dust | Free | Not needed | FIXSee the answer: An old or dusty thermostat |
2026 U.S. averages, rounded. Pro prices include parts and labor. Most companies charge $75–$250 to come out, and many put that toward the repair. Nights, weekends and big cities cost more. See all repair prices
Want proof it's the thermostat, not the furnace?
The 5-minute test
This tells you whether the thermostat is asking for heat or cooling.
- Set the mode to Heat or Cool.
- Set the temperature 5 degrees past the room: above for heat, below for cooling.
- Wait at least 5 minutes. Don't keep changing it. Then look at the screen.
- The furnace or AC starts: the thermostat works. Check your settings and schedule.
- Heat On or Cool On is steady, but nothing starts: the thermostat is asking. The problem is likely in the furnace or AC.
- Neither shows, and nothing starts: it may be the thermostat or its wiring. Take the questions at the top.
Not sure it's safe to keep trying?
Stop and call a pro if…
- You smell gas or rotten eggs. Leave the house first, then call the gas company from outside.
- The furnace or AC breaker trips again after one reset.
- The thermostat's wires are loose or damaged.
- Water keeps backing up in the drain pan.
- You smell burning from the furnace or AC.
Never tape or hold in the furnace door switch. Honeywell says not to tape, bypass or disable it.
Got a quote for a new thermostat?
Fix it, or get a new thermostat?
Honeywell says to troubleshoot before you replace a thermostat. Most problems are batteries, power or a setting. When you do need a new one, HomeGuide lists $140–$350 installed, about $229 on average. Ask yourself three things:
- How old is it? HomeGuide says thermostats usually last about 10 years.
- Staying with Honeywell? HomeGuide lists Honeywell smart thermostats at $99–$229, or $200–$430 installed.
- Which kind? A basic one installed runs about $100–$200. A smart one runs about $185–$600, and may need a C-wire ($90–$135).
- Is the thermostat really the problem? If it clicks but nothing runs, a new thermostat won't help. The furnace or AC needs a look.
Example: about $230 to install a new programmable thermostat is typical. A quote for a new furnace because the thermostat screen went blank is worth a second opinion.
Ran into a word you don't know?
Honeywell thermostat words, explained
Read these before you start. The drawings show roughly what each part looks like.
- Thermostat
- The control on your wall that tells the furnace and AC when to run.
- Mode
- Heat, Cool, Off or Auto. It tells the thermostat which job to do.
- Hold
- A setting that keeps one temperature and ignores the schedule.
- Heat On / Cool On
- Words on a Honeywell screen. Steady means it's calling for heat or cooling. Flashing means it's waiting.
- Faceplate and wall plate
- The thermostat snaps onto a plate on the wall. The wires connect to the plate.
- Jumper switch (R/Rc)
- A small switch on some Honeywell wall plates. It's set by how many power wires you have.
- C-wire
- A wire that gives the thermostat steady power from the system. Smart thermostats often need one.
- Furnace switch
- A light switch on or near the furnace, often on a red plate. It turns the furnace's power on and off.
- Door safety switch
- A button behind the furnace's front panel. If the panel is loose, it cuts the power.
- Breaker
- A safety switch in your breaker box. The furnace and AC each usually have their own.
- Float switch
- A small switch by the drain pan. It cuts power if water backs up.
- Condensate drain
- The small pipe or hose that carries water away from your AC or high-efficiency furnace.
- Compressor
- The part in the outdoor AC unit that does the cooling. Systems wait a few minutes before restarting it.
Still have questions?
Questions people ask most
Why is my Honeywell thermostat blank?
When a Honeywell thermostat is blank, Honeywell says to start with the batteries. If it's wired, check that the furnace door is closed, its switch is on, and the breakers are on. Then push it firmly onto its wall plate.
Is a Honeywell thermostat that's not working an emergency?
A Honeywell thermostat that's not working is not an emergency in itself, but a gas smell is. Leave the house without touching the thermostat or any switches, and call the gas company from outside. No heat in freezing weather is urgent, so try the checks at the top and call a pro today if the heat won't come on.
Why is "Cool On" or "Heat On" flashing on my Honeywell?
A flashing Cool On or Heat On means your Honeywell is waiting through a built-in delay. Honeywell says to wait 5 minutes for the system to safely respond. HoneywellStore.com says the pause protects the AC's compressor.
Why won't my Honeywell work after I changed the batteries?
A Honeywell that won't work after new batteries usually isn't pushed all the way onto its wall plate. Or a battery may face the wrong way. HoneywellStore.com says to reset the date, time or schedule if it asks.
Why won't my new Honeywell thermostat turn on?
If a new Honeywell thermostat won't turn on, Honeywell says to check that a C wire is connected at both the thermostat and the furnace. If your model has a jumper switch, set it to 1 Wire or 2 Wire to match your R and Rc wires. Turn off the furnace's power first.
Who do I call about a Honeywell thermostat? How do I contact Honeywell?
If your Honeywell thermostat is under warranty, contact Honeywell Home first. Its support page has live chat, and its tech support line is 1-800-633-3991. Out of warranty, or if the furnace or AC is the problem, call a local heating and cooling company. The pros we list aren't approved by Honeywell.
What do I do with an old round Honeywell thermostat?
Don't throw an old round Honeywell thermostat in the trash. HomeGuide says thermostats from before 2002 may contain mercury. Take it to a hazardous waste drop-off or an HVAC supplier.
How much does a new Honeywell thermostat cost?
A new Honeywell smart thermostat costs $99–$229, or $200–$430 installed, according to HomeGuide. A thermostat installed runs about $140–$350 on average.
How we built this
The questions follow Honeywell Home's own troubleshooting order: batteries, then power to the furnace or air handler, then the mode and setpoint, then what the screen shows. Each answer makes some causes more likely and others less likely.
Prices are 2026 national averages from published repair-cost guides, rounded. Your local prices will differ.
- Honeywell Home, why won't my thermostat screen power up (updated September 2025)
- Honeywell Home, how do I fix a blank display on my RTH6360 thermostat (updated September 2025)
- Honeywell Home, why is my heat not working (updated September 2025)
- Honeywell Home, why is my cooling system not working (updated September 2025)
- Honeywell thermostat not working: troubleshooting guide, HoneywellStore.com, run under license from Honeywell (read October 2026)
- Carrier, reasons your furnace is blowing cold air (read October 2026)
- HomeGuide, thermostat installation cost (August 2025)
- HomeGuide, drain cleaning cost, including AC drain lines (December 2025)
- Fixr, thermostat installation cost (February 2026)
About Honeywell: StuffBreaks is independent and not affiliated with Honeywell. Honeywell is a trademark of its owner. Where Honeywell's own instructions differ from general advice, this page follows Honeywell's. They come from Honeywell Home, why won't my thermostat screen power up? (checked October 9, 2026).
How we make money: some links go to parts stores that pay us a small commission, and some pro listings pay us when you call them. Verdicts come from the diagnosis, not from who pays more.