Direct answer
Separate thermostat demand, household power, airflow, ignition and safety lockout before changing controls. A repeated ignition or limit fault requires service.
What this covers
- Residential forced-air furnaces with customer-accessible thermostat, power, filter and indicator checks
- The exact condition described in the title
- Customer-accessible checks before internal repair or reset
What it does not cover
- ×A different brand, model family or similar-looking code
- ×Internal live-electrical, gas, refrigerant or sealed-system testing
- ×A guarantee that a named component has failed without isolation
Capture the exact state
ReversibleSet a clear heat demand and record thermostat, blower, burner and indicator state.
Separate the likely fault domains
ReversibleCheck the service switch, breaker once, correct filter, open supply/return paths and exact panel legend.
Correct only the proven, accessible condition
ReversibleRestore an obvious power or airflow condition and perform one normal restart.
Verify once before going farther
ReversibleConfirm a full heat cycle starts, satisfies demand and stops normally.
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 record first for “Furnace runs or calls for heat but the house stays cold”?+
Set a clear heat demand and record thermostat, blower, burner and indicator state.
Does the symptom or code prove a part has failed?+
No. Check the service switch, breaker once, correct filter, open supply/return paths and exact panel legend.
When should I stop troubleshooting?+
Leave and contact the gas utility for gas odor; stop for soot, flame rollout, CO alarm, smoke or damaged venting.
Answer for the exact device and software version shown above.