Thermostat display shows A01 and boiler does not ignite when there is a call for heat.

Safety first: You are working with a control that communicates with a gas boiler. Do not open the boiler casing unless you are a qualified technician. You may work on low‑voltage thermostat wiring only with power isolated.

• Reset the boiler and thermostat:
  • Turn the boiler off at the main switch and isolate power for 30 seconds.
  • Turn the Ferroli smart thermostat off (if it has a power button) or remove it from its base for 30 seconds.
  • Restore power to the boiler, then refit/power the thermostat and check if A01 clears.
• Check communication wiring:
  • Isolate power to the boiler and thermostat.
  • Locate the OT/OpenTherm or BUS terminals on the boiler and on the Ferroli smart thermostat receiver/base.
  • Verify the two‑core cable is firmly clamped, not reversed (if polarity is required by your model), and not damaged or pinched.
  • Tighten any loose terminal screws.
• Verify thermostat settings:
  • In the thermostat menu, confirm the control mode is set to OpenTherm/Bus (not simple on/off) if your boiler supports it.
  • Ensure the heating schedule is active and the setpoint is above room temperature.
• If A01 persists:
  • The boiler may have a genuine ignition fault (electrode, gas valve, or PCB). Do not attempt to repair the boiler yourself.
  • Contact a qualified Ferroli service technician and report that the thermostat shows A01 and the boiler is in ignition lockout.