Boiler shows error 31, communication error with remote control or external interface.

Safety: Isolate power before working on control wiring.

• Check controller wiring: Verify that the two-wire bus from the Immergas room controller is connected to the correct terminals and that polarity is observed if required by the model.
• Inspect cable: Look for damage, joints, or extensions that may cause interference. Use twisted pair cable as recommended.
• Test without controller: Temporarily disconnect the controller and fit a standard link or basic thermostat as per the manual. If the boiler works without error 31, the controller or its wiring is suspect.
• Replace controller: If wiring is sound, replace the Immergas controller with a compatible new unit.
• PCB check: If communication errors persist with a known-good controller, the PCB bus interface may be faulty and require replacement.