Viessmann A9

Critical

Vitocal — Compressor switched off, heating via alternative source.

Viessmann A9: Compressor switched off, heating via alternative source. This fault typically halts operation and needs immediate attention.

Possible causes

Heat pump faulty or safety high-pressure switch (C9) tripped.
Flow/return sensors faulty for over 24 h.

Check steps

Check message history of heat pump.
Check flow rates & primary/secondary sensors.

Affected parts

Temperaturfühler
Sicherheitshochdruckschalter

Safety note

De-energise; refrigerant circuit by technician only.

Source: Viessmann resmi servis kılavuzu — Serviceanleitung Vitotronic 200 Typ WO1C (Viessmann community PDF, 2017-01 ed., p.103 'A9 Wärmepumpe'; identical in intec-heizung mirror): 'Verdichter wird ausgeschaltet. Raumbeheizung und Trinkwassererwärmung erfolgt mit anderen, dafür freigegebenen Wärmequellen, z. B. externer…

Reviewed by Anıl Güzeldemir — in the refrigeration machine room since 2006, developer of Enthalio.

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Related fault codes

Safety high-pressure switch tripped, compressoC9 Low-pressure fault, compressor switches off.D3 Control high-pressure fault, compressor off.D4 Flow switch detects no flow, compressor off.D6 Utility lockout – compressor off (by energy suC5 Primary-circuit protection – compressor off.CA