Boiler displays A03, water pressure too low, boiler will not start.

Safety: Do not overfill the system. Typical cold pressure is around 1.0–1.5 bar; check your Immergas manual.

• Top up pressure: Locate the filling loop under the boiler. Open the valves slowly until the pressure gauge reaches the recommended value, then close both valves.
• Bleed air: Bleed radiators and re-check pressure, topping up again if needed.
• Check for leaks: Inspect radiators, valves, and visible pipework for signs of water. Repair leaks promptly.
• Sensor check: If the gauge shows correct pressure but A03 persists, the pressure sensor may be faulty and should be replaced by a technician.