59 on a Viessmann Vitotronic 200: Electronic expansion valve faulty

What it means

The manuals for this range word it in different ways:

• Electronic expansion valve faulty.
• Electronic expansion valve for suction gas superheating faulty.

Part involved: Electronic expansion valve faulty; Electronic expansion valve for suction gas superheating faulty.

When it shows: Type "Fault" (S) - triggers "05 Refrigerant circuit" on the heat pump control unit. Heat pump characteristics: Compressor OFF.

Likely causes:

• Electronic expansion valve faulty.
• Electronic expansion valve for suction gas superheating faulty.

Is it safe?

The heat pump stops until the fault clears or is reset.

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

• Check plug at connection J7: See "EEV PCB [4-3] / [4-4] ".
• Check stepper motor of electronic expansion valve.
• Check plug at connection J7: See "EEV PCB [4-6] / [4-7] ".
• Check plug at connection J11: See "EEV PCB [4] ".

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

• No heating
• No hot water
• Keeps stopping / cutting out

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, 163 · Reviewed 23 September 2026

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

Reviewed: 23 September 2026