Boiler shows 105, frequent overheat lockouts, loud kettling noises from boiler

Safety: Turn off power and gas before removing covers. Surfaces may be very hot.

• Check system pressure and bleed: Ensure pressure is 1.0–1.5 bar cold. Bleed radiators and the pump to remove air.
• Listen for kettling: Boiling or banging noises from the primary heat exchanger indicate limescale or poor flow. This is common in hard water areas.
• Descale primary circuit: A professional can circulate a descaling solution through the primary heat exchanger. As a homeowner, you can add inhibitor and cleaner to reduce further build-up, but internal descaling should be done by an engineer.
• Check pump performance: If radiators heat slowly and the boiler overheats, the pump may be weak. Replacement of the Ariston pump assembly is often required.
• Adjust boiler output: On some Ariston models, the maximum CH output can be reduced via the control panel or PCB potentiometer. Setting it too high for a small system can cause short cycling and overheating. Refer to the installation manual; adjustments should be made by a competent person.