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us Home & property emergencies thermostat screen blank • thermostat error code • furnace not starting • ac not starting • no heat thermostat dead • thermostat not turning on • hvac lost power • thermostat batteries dead • smart thermostat offline • thermostat black screen • breaker tripped hvac • furnace won’t turn on • air handler not running • condensate float switch • carbon monoxide alarm • smell gas in home • thermostat reset • heating cooling won’t start • hvac safety shutoff

What to do if…
your thermostat screen goes blank or shows an error and heating or cooling won’t start

Short answer

Assume it’s a power or safety shut-off first: stop repeated resets, check batteries and HVAC power, and if there’s any gas smell or a carbon monoxide alarm, get outside and call 911 and/or your gas utility’s emergency number.

Do not do these things

  • Don’t keep flipping the system on/off or doing repeated resets.
  • Don’t bypass safety devices or “jump” thermostat wires to force the unit to run.
  • Don’t keep resetting a breaker that won’t stay on.
  • Don’t touch switches/breakers if you smell gas or a CO alarm is sounding—leave first.

What to do now

  1. Check for immediate danger first (before touching switches).

    • If you smell gas or suspect a leak: leave the home, get to fresh air, then call 911 and/or your gas utility’s emergency number from a safe location.
    • If a carbon monoxide (CO) alarm sounds: move outside to fresh air and call 911 (or your local fire department). Do not re-enter until responders say it’s safe.

  2. Restore thermostat power (fastest fix).

    • Replace thermostat batteries with fresh ones (even if you replaced them recently).
    • If the thermostat snaps onto a baseplate, press it firmly back into place.
    • If it’s a smart thermostat: confirm any receiver/equipment module has power and the outlet hasn’t been switched off.

  3. Confirm your HVAC system has power (only if there’s no gas/CO concern).

    • Check your electrical panel for a tripped breaker labeled Furnace / Air Handler / HVAC / AC.
    • Look for a nearby wall switch by the furnace/air handler (often looks like a light switch) and make sure it’s ON.

  4. If the thermostat shows an error code, capture it.

    • Take a photo of the thermostat error message/code.
    • If the furnace/air handler has a display window or diagnostic light visible without removing panels, note what you can see (don’t open anything).

  5. Try one clean restart (once).

    • After restoring power/batteries, wait 2–5 minutes for the thermostat to boot and call for heating/cooling.
    • If you reset a breaker, give the system a few minutes—some equipment has built-in start delays.

  6. If it still won’t run, assume a safety shut-off and stop restarting.

    • Common examples include a condensate overflow/float switch (clogged drain) or an internal safety lockout.
    • The safe move is to stop resets and call HVAC service, especially if the breaker trips again or you see repeated error codes.

  7. Stabilise safely while you wait.

    • Heat: use layers/blankets and close doors to concentrate warmth in one room.
    • Cooling: shade windows, use fans, and stay hydrated.
    • Do not run grills, generators, or other fuel-burning devices indoors.

What can wait

  • You do not need to decide now whether the thermostat needs replacement.
  • You do not need to open the furnace/air handler, touch wiring, or troubleshoot beyond batteries and obvious power checks.
  • You do not need multiple resets—one restart is enough before you escalate.

Important reassurance

A blank thermostat screen is often a simple loss of power (dead batteries or HVAC low-voltage power being cut). Taking a photo of any codes and avoiding repeated resets helps prevent worsening a lockout and speeds up repair.

Scope note

This is first-step guidance to get you safely back to heating/cooling or to a clear handoff to HVAC service. Repeated lockouts, breaker trips, gas smells, or CO alarms need urgent, qualified help.

Important note

This is general information, not professional advice. If you smell gas or a CO alarm sounds, prioritize getting outside and contacting emergency services and/or your gas utility.

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