H1 is shown on the display and the unit stops blowing warm air in heating mode; outdoor unit may frost up.

Note: On many Bosch heat pump models, H1 indicates normal defrost, not a fault.

What to do:

• Wait 5–15 minutes: During defrost, the indoor fan may slow or stop and H1 is displayed. This is normal. Heating will resume automatically.
• Check outdoor coil: If the outdoor coil is heavily iced over even after defrost, ensure the coil is clean and that the outdoor fan is operating correctly.
• Improve drainage: Make sure meltwater can drain away from the outdoor unit and is not refreezing around the base.

If H1 is constant or heating is poor: A technician should check the defrost sensor, reversing valve operation, and refrigerant charge.