Slant/Fin Error Lockout 138 / Alert 448: Flame too low — burner shut down on weak flame signal
The control sensed a flame signal too weak to safely continue and shut the burner down (Lockout 138 = 'Flame too low'; Alert 448 = 'Flame too low' reports the same weak-flame condition informationally, and Alert 449 notes the minimum modulation rate was temporarily raised due to low flame strength). The Slant/Fin CHS manual's documented cause for code 138 is blocked venting — check the exhaust-vent, air-inlet, combustion blower, gas-valve venturi, and heat exchanger for blockage; a fouled flame sensor or incorrect combustion settings can also produce a weak flame signal. We diagnose and repair it across Greater Vancouver — same-day and after-hours.
The control sensed a flame signal too weak to safely continue and shut the burner down (Lockout 138 = 'Flame too low'; Alert 448 = 'Flame too low' reports the same weak-flame condition informationally, and Alert 449 notes the minimum modulation rate was temporarily raised due to low flame strength). The Slant/Fin CHS manual's documented cause for code 138 is blocked venting — check the exhaust-vent, air-inlet, combustion blower, gas-valve venturi, and heat exchanger for blockage; a fouled flame sensor or incorrect combustion settings can also produce a weak flame signal.
Slant/Fin fault codes can vary by model and series. Use this as a guide — the same code can have more than one cause. Our Technical Safety BC–licensed technicians read the code, confirm it against your unit's manual, and diagnose the true cause before any repair.
Likely causes of Slant/Fin error Lockout 138 / Alert 448
- Blocked exhaust vent, air intake, blower, venturi, or heat exchanger
- Fouled or cracked flame sensor (flame rod) giving a weak signal
- Incorrect or drifted combustion settings
- Dirty heat exchanger reducing combustion quality
What you can safely check
- Check the outside vent and intake terminals for blockage (snow, ice, debris)
- Confirm the condensate drain is flowing freely
Beyond these checks, do not open the unit or touch gas/electrical parts — BC law requires a licensed gas fitter. Call us for a proper diagnosis.
Error Lockout 138 / Alert 448 usually leaves you without heat or hot water and can indicate a safety-related fault. Don't keep resetting it — call for priority after-hours Slant/Fin repair.
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Parts often behind Slant/Fin error Lockout 138 / Alert 448
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Slant/Fin Error Lockout 138 / Alert 448 Repair Across Metro Vancouver
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