Boiler shows A04, will not start, pressure gauge indicates low or zero pressure

Safety: Ensure the boiler is cool before adding water. Do not exceed the maximum pressure indicated in the Fondital manual (usually around 2.0 bar cold).

Steps:

• Check for visible leaks: Inspect radiators, valves, and pipework around the boiler for drips or stains.
• Top up pressure: Locate the filling loop (flexible hose or built-in valve) under the Fondital boiler. Slowly open the valves until the pressure gauge rises to about 1.2–1.5 bar, then close both valves tightly.
• Bleed radiators: Bleed air from radiators starting from the lowest floor. Recheck pressure and top up again if needed.
• Reset the boiler: Use the reset control. If A04 persists with correct pressure, a sensor fault is likely.

Technician actions:

• Test and replace the water pressure sensor / pressure switch on the hydraulic group if it does not read correctly.
• Inspect and replace a leaking automatic air vent or safety valve.
• Check the expansion vessel pre-charge and diaphragm; recharge or replace if failed.