Smart home · HVAC

Smart thermostat says heating but the furnace is not running

A heat call on screen does not prove the HVAC received power/control. Check mode, setpoint, equipment delay, breaker/service switch and furnace fault light without bypassing controls.

Direct answer

A heat call on screen does not prove the HVAC received power/control. Check mode, setpoint, equipment delay, breaker/service switch and furnace fault light without bypassing controls.

What this covers

  • The observed symptom matches this record
  • Customer-accessible settings, connections and external components
  • Diagnosis before reset, deletion or component replacement

What it does not cover

  • ×A model-specific error code with a different documented meaning
  • ×Internal electrical, battery-cell, gas, refrigeration or sealed-component repair
  • ×A guarantee that every model exposes the same control label
Try in this order0 of 4 completed
  1. Capture the exact symptom

    Reversible

    Raise setpoint modestly and note thermostat relay indication, delay message and furnace status light.

  2. Run the smallest isolation test

    Reversible

    Confirm HVAC breakers and service switch, closed panels and any condensate safety condition.

  3. Correct only the proven cause

    Reversible

    Correct only external power/configuration; have an HVAC technician test low-voltage wiring, safeties and ignition.

  4. Verify before changing anything else

    Reversible

    Run one complete heat cycle and confirm supply air warms and stops at setpoint.

Evidence ledger

Sources behind this answer

Visible sources support the visible claims. Home Product Support records the publisher, the fact used and the review date; community reports can suggest an issue but do not become a published fact on their own.

Exact questions

Common follow-ups

What should I check before resetting anything?+

Raise setpoint modestly and note thermostat relay indication, delay message and furnace status light.

What is the safest isolation test?+

Confirm HVAC breakers and service switch, closed panels and any condensate safety condition.

When should I stop troubleshooting?+

Leave the home and call emergency services for gas odor or carbon-monoxide alarm; never jumper safety terminals.

Change recordAug. 17, 2026 — Published as an independently scoped question with a distinct isolation test, verification and safety boundary; source boundary: ecobee Support.
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