An HVAC that turns on but doesn’t heat usually points to airflow, thermostat, or ignition/heat‑source faults. The most common real-world cause is a dirty air filter or an incorrect thermostat mode that keeps the system from producing heat. A furnace can also overheat and open a safety limit, so the blower keeps running but only cold air comes out. Heat pumps may run without heat if the outdoor unit can’t transfer heat or the reversing valve isn’t switching. On service calls around Sachse, we often find settings-related issues after weather swings. A quick check can save time before a technician visit.
Look for these specific signals:
- Thermostat left on Cool or Fan, or set too low
- Very dirty filter or closed supply/return vents
- Gas furnace: failed igniter, dirty flame sensor, or gas valve off
- Heat pump: iced outdoor coil, low refrigerant, or stuck reversing valve
- Electric heat: tripped breaker or failed heat strips
If you smell gas, see repeated breaker trips, or notice a burning smell, shut the system off and schedule a professional inspection immediately.
Updated: 2026-03-30
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