Error 04 displayed; water heater shuts down shortly after starting, often accompanied by gurgling noises.

Safety: Turn off power and allow the unit to cool completely before touching internal components.

Steps:

• Bleed air from system: If connected to a heating circuit, bleed radiators and any manual air vents near the water heater. Low circulation can cause local overheating.
• Check system pressure (for sealed systems): Verify the pressure gauge reads within the Biasi-specified range (typically around 1.0–1.5 bar when cold). Top up via the filling loop if allowed by the manual.
• Inspect pump operation: With the cover removed and power restored, call for heat and feel the circulation pump. It should vibrate slightly and the connected pipes should warm evenly. If the pump is silent or extremely hot, it may be seized.
• Clean primary heat exchanger (visual): Look for heavy scale or sludge deposits on the water side connections. Severe fouling requires professional chemical cleaning or replacement.

Note: A repeatedly tripping high-limit or flue thermostat indicates a serious circulation or combustion issue. Contact a Biasi service technician for sensor testing and heat exchanger descaling.