Error H51 displayed; the heater may shut down during operation.

Safety: Turn off power. Be cautious when opening valves; hot water may be present.

• Check system pressure: Read the pressure gauge on the heater or system. Compare to the recommended cold fill pressure in the Buderus manual.
• Top up system: If pressure is low, open the filling loop or make-up valve and slowly add water until the correct pressure is reached. Close the valve securely afterward.
• Bleed air: Bleed radiators or air vents to remove trapped air, then recheck pressure and top up if needed.
• Inspect for leaks: Look for visible leaks at valves, joints, and around the heater. Repair any leaks found.
• Check pressure sensor: If pressure is correct but H51 persists, test the water pressure sensor according to Buderus procedures and replace if faulty.
• Restore and test: Restore power and verify that H51 clears and that the heater operates normally.