Boiler displays SFL or Soft Lockout; unit stops firing but may restart after a delay or reset.

Safety first: Soft lockouts are safety-related. Do not repeatedly reset without investigating. Turn off power and gas if you suspect a combustion problem.

• Note the pattern: Observe when SFL occurs—during ignition, mid-burn, or at shutdown. This helps identify whether ignition, flame sensing, or airflow is the root cause.
• Clean flame sensor and check ground: Remove and clean the flame rod as described for FL faults. Ensure all ground wires are tight and free of corrosion.
• Inspect venting and air intake: Confirm that intake and exhaust are clear and properly installed. Wind or recirculation at the termination can cause unstable flame.
• Reset and monitor: After addressing obvious issues, reset the boiler and monitor operation. If SFL returns, stop resetting and call a technician.

When to call a professional: Soft lockouts that recur indicate underlying combustion or control issues that require professional combustion analysis and diagnostics.