Boiler will not fire, control display shows E01 lockout

Safety first: Turn off electrical power to the boiler at the service switch and shut off the gas supply valve before removing any covers. If you ever smell gas, evacuate and call your gas utility or a licensed technician immediately.

Step-by-step checks:

• 1. Verify gas supply: Confirm the manual gas shutoff valve to the boiler is fully open. Check that other gas appliances in the home work. If no gas anywhere, contact the gas utility.
• 2. Reset the boiler: Restore power, then press the reset button on the Slant/Fin control (or cycle power off for 30 seconds and back on). If E01 returns immediately, continue below.
• 3. Inspect the igniter: With power off, remove the burner access panel. Locate the hot surface igniter or spark igniter assembly. Look for cracks, chips, or heavy white scaling. If damaged, replace the igniter with the exact Slant/Fin-specified part.
• 4. Check flame sensor: If separate from the igniter, remove the flame rod and gently clean it with fine steel wool or emery cloth to remove oxidation. Reinstall and ensure the ceramic insulator is not cracked.
• 5. Inspect wiring and connectors: Verify all low-voltage and high-voltage connectors between the ignition control module and the gas valve, igniter, and flame sensor are tight and not corroded or burned.
• 6. Gas valve operation: With a manometer and proper training, a technician should verify inlet and manifold gas pressures while the boiler attempts to fire. If the gas valve does not open when commanded, it may be defective.

When to call a professional: If E01 persists after cleaning the flame sensor and confirming gas supply, or if you are not trained to work on gas ignition systems, contact a licensed boiler technician. Misdiagnosis can lead to unsafe combustion.