Error 501, no flame detected after ignition attempts, repeated lockouts.

Safety: If you smell gas, do not attempt to light any appliance. Ventilate the area and contact your gas supplier.

• Verify gas supply: Check that the gas isolation valve near the furnace is open. Confirm other gas appliances work.
• Reset the furnace: Follow the Ariston manual to reset from lockout. Observe whether the fan runs, you hear clicking, and whether the burner lights.
• Clean burner and electrodes: With power and gas OFF, remove the burner cover. Clean burner ports and the ignition/flame sensor assembly as described in earlier steps.
• Check gas valve wiring: Inspect the multi-pin connector on the gas valve for secure fit and no signs of overheating.

If 501 persists after basic cleaning and checks, gas valve and combustion adjustments must be handled by a qualified Ariston technician with proper test equipment.