Viessmann Defrost / Anti-Cold Air Protection (Informational)

Heating mode delayed; H1 displayed; outdoor unit not starting immediately

Possible Causes

System in defrost cycle, Low outdoor temperature, Indoor coil not yet warm enough to start fan, Normal protection logic

Note: H1 on many Viessmann heat pump models is an informational code, not a fault.

Allow time: Wait several minutes for the defrost or anti-cold-air cycle to complete. The indoor fan will start once the coil is warm.
Check filters and coil: Ensure indoor and outdoor coils are clean to minimize defrost duration.
Monitor operation: If H1 remains for an unusually long time or heating never resumes, have a technician check defrost sensors and control logic.

Very Easy 1/5