45
Carrier
Control Circuit Lockout
Furnace LED shows code 45 (control circuit lockout). Furnace is non-responsive until power is cycled.
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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 failed ignition attempts, repeated limit trips, internal control board fault, low line voltage
How to Fix / Troubleshooting
Safety first: Turn off power and gas before inspection.
- Power cycle: Turn off the furnace service switch or breaker for at least 30 seconds, then turn it back on. This often clears a temporary lockout.
- Review recent codes: Many Carrier boards flash the last fault code before 45. Note any previous codes (e.g., 33, 34) and address those underlying issues first.
- Check line voltage: Verify that the furnace is receiving stable 120V. Flickering lights or frequent breaker trips may indicate electrical issues.
- Inspect board for damage: Look for burned spots, swollen components, or corrosion on the control board.
If lockouts recur after addressing other faults, the control board may need replacement by a qualified technician.
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Repair Difficulty
Hard
4/5
Required Part
Furnace Control Board
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