Display shows A04, no burner operation, boiler indicates low water pressure

Safety: Allow the system to cool before topping up. Do not overfill beyond the recommended pressure.

• 1. Read pressure gauge: Check the manometer on the Brötje boiler. If below the minimum (often ~0.8 bar), the boiler will lock out with A04.
• 2. Top up system: Connect the filling loop hose (if external) between the mains water and heating return connection. Open the valves slowly and watch the gauge rise to the target cold pressure (typically 1.2–1.5 bar). Close both valves and remove the hose if required by local regulations.
• 3. Bleed radiators: After filling, bleed air from the highest radiators and recheck pressure, topping up again if needed.
• 4. Check for leaks: Inspect all visible radiators, valves, and boiler connections for signs of water. Repair any leaks before repeated refilling to avoid corrosion.
• 5. Expansion vessel check: If pressure rises too high when hot and drops to zero when cold, the internal or external expansion vessel may have lost charge or have a ruptured diaphragm. A technician should measure and recharge or replace the Brötje expansion vessel.
• 6. Pressure sensor: If the gauge shows correct pressure but A04 persists, the electronic pressure sensor may be faulty and require replacement.