6A on a Viessmann Vitotronic 200: Air intake temperature too low

What it means

The manuals for this range word it in different ways:

• Air intake temperature too low.
• Primary inlet temperature (brine inlet) too low.

Part involved: Air intake temperature too low; Primary inlet temperature (brine inlet) too low.

When it shows: Type "Note" (H) - triggers "07 Refrigerant circuit" on the heat pump control unit. Heat pump characteristics: Compressor does not start.

Likely causes:

• Air intake temperature too low.
• Primary inlet temperature (brine inlet) too low.

Is it safe?

The manual does not say whether the heat pump stops.

Resetting itself: Not stated in 6150133.

Manual reset: Refrigerant circuit messages cannot be acknowledged in the message history (6150133 p.155); acknowledge the resulting 05/07/A9 message on the control unit.

What you can check

• This code is only visible to engineers in the service menu (Diagnosis > Refrigerant circuit > Message history); homeowners see message 05, 07 or A9 - note that code and call your contractor.

What the engineer will check

• No action required.
• As for "CB Flow temp. primary" : See "Message overview" for the heat pump control unit.

Who to ask for: Viessmann-trained heat pump engineer with F-gas refrigeration certification.

Certification: F-gas certificate (UK F-gas Regulations; Viessmann: refrigerant work by authorised refrigeration engineers only).

What you might notice

• Insufficient heating (house not warm enough)

Sources

• Service instructions Vitotronic 200 type WO1C heat pump control unit (air/water split & monobloc, brine/water) (6150133, 2023-07) ↗ · 6150133 VSA00004 · pages 169, 175 · Reviewed 23 September 2026

A code explains what the controller detected, not a confirmed root cause.

Reviewed: 23 September 2026