How to Fix / Troubleshooting

Safety: Turn off power and allow the system to cool before adding water. Hot water under pressure can cause scalding.

Steps:

Check pressure gauge: On hydronic Buderus furnaces/boilers, read the system pressure. Typical cold pressure is around 1.0–1.5 bar (check your manual).
Open fill valve: If your system has a manual fill valve, slowly open it to add water until the gauge reaches the recommended pressure. Close the valve afterward.
Inspect for leaks: Walk the system and look for visible leaks at radiators, valves, and under the furnace. Repair leaks before repeatedly refilling.
Bleed air: After refilling, bleed air from radiators and high points, then recheck pressure.
Check pressure sensor wiring: Ensure the Buderus pressure sensor connector is secure on the control board.

If H1 persists with correct pressure, the pressure sensor may be defective and should be replaced.

Display shows H1, furnace locked out, no burner operation

Possible Causes