Carrier
General System Lockout Indication
Thermostat indicates 'System Malfunction' or 'Call for Service' without a specific code, and system may be locked out.
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Safety Warning
This repair may involve working with high voltage components or water connections. Always unplug the appliance before removing any panels.
If you are not confident in your ability to perform this repair safely, we strongly recommend contacting a professional technician.
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Possible Causes
Multiple recent safety trips on Carrier furnace or heat pump, High- or low-pressure switch trips, Flame failure lockout, Repeated ignition failures
How to Fix / Troubleshooting
Safety first: Turn off power to the HVAC system before opening any equipment panels.
- Step 1 – Power cycle: Turn off breakers to indoor and outdoor units for 5 minutes, then restore power to clear temporary lockouts.
- Step 2 – Check equipment LEDs: Inspect the Carrier furnace or outdoor unit for diagnostic LEDs and note any blink codes. Refer to the equipment manual for meanings.
- Step 3 – Inspect filters and coils: Ensure filters are clean and outdoor coil is not blocked by debris.
- Step 4 – Observe operation: After reset, monitor the system. If it quickly returns to malfunction status, a persistent fault exists.
- When to call a pro: Safety-related lockouts (flame, pressure, limit) should be diagnosed by a qualified technician.
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Repair Difficulty
Hard
4/5
Required Part
Carrier Furnace/Heat Pump Safety Controls
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