Thermostat intermittently shows F03 and loses connection to the boiler; heating stops unexpectedly.

Safety first: Isolate power to the boiler and thermostat receiver before touching any wiring.

• Check BUS wiring:
  • Locate the BUS/OpenTherm terminals on the boiler and on the Ferroli receiver.
  • Ensure the two‑core cable is connected to the correct terminals on both ends.
  • Tighten terminal screws and ensure no copper strands are shorting between terminals.
• Separate from mains cables:
  • If the BUS cable runs in parallel with 230 V mains cables, reroute it or increase separation to reduce interference.
• Power cycle and re‑pair:
  • Turn off power to boiler and receiver for 1 minute.
  • Restore power and, if applicable, re‑pair the wireless room unit with the receiver following the Ferroli instructions.
• If F03 persists:
  • The BUS interface on the receiver or boiler PCB may be defective.
  • Contact a Ferroli service technician; they may need to replace the Ferroli BUS receiver module or boiler PCB.