Furnace will not start; control shows E01 shortly after a call for heat.

Safety first: Turn off electrical power to the furnace at the service switch and shut off the gas supply before removing panels. Allow the furnace to cool.

• Inspect flame sensor: Remove the burner access panel. Locate the flame sensor (usually a small metal rod in front of a burner, wired back to the control). Remove the mounting screw and gently clean the rod with fine steel wool or a Scotch-Brite pad until shiny. Do not sand heavily. Reinstall and reconnect the wire.
• Check hot surface igniter: Visually inspect the igniter (ceramic base with a glowing element). If it is cracked, white and chalky, or does not glow during a call for heat, it is likely failed. Test with a multimeter for continuity. Replace if open.
• Verify gas supply: Confirm the manual gas shutoff valve near the Wolf furnace is parallel to the pipe (open). If you have other gas appliances, verify they operate normally. If not, contact your gas supplier.
• Reset and test: Restore power and gas. Set the thermostat to call for heat and observe the ignition sequence through the sight glass. If E01 returns after cleaning the sensor and confirming gas, the ignition control section of the Wolf main control board may be faulty and should be diagnosed or replaced by a qualified technician.