Display shows A04, burner does not start, often after overheating or poor circulation.

Safety: Allow the heater to cool completely. Turn off power before removing covers.

• Check system pressure: On combination Fondital boilers/water heaters, verify the system pressure gauge (if present) reads within the recommended range (typically 1.0–1.5 bar when cold). Refill via the filling loop if low, following the manual.
• Bleed air: Bleed radiators and any automatic air vents in the system to remove trapped air that can cause local overheating.
• Verify pump operation: With the unit calling for heat, listen and feel for vibration at the circulation pump. If it is silent or extremely hot to the touch, it may be seized or air‑locked. Gently vent the pump via its bleed screw (if fitted) with power OFF and a cloth ready for water.
• Reset overheat thermostat: Some Fondital models have a manual reset button on the overheat thermostat mounted on the heat exchanger. Press only after restoring circulation and ensuring no blockage.
• Descale heat exchanger: If overheating recurs, the primary heat exchanger may be scaled or sludged and should be chemically cleaned or replaced by a professional.