99 on a Viessmann Vitotronic 200: Current difference of the individual phases on the compressor too high
Short answer
On a Viessmann heat pump, 99 means: Current difference of the individual phases on the compressor too high. The heat pump stops until the fault clears or is reset. An engineer is needed to fix the cause.
Reviewed 23 September 2026 · 1 source
What it means
The manuals for this range word it in different ways:
- Current difference of the individual phases on the compressor too high.
- Vitocal 300-G/333-G: Current difference of the individual phases on the compressor too high.
- Current difference of power factor correction filter too high (> 10 A).
- Solar module sensor 10: No switching of the appliance connected at plug sS of the solar control module, type SM1 (circulation pump or 3-way diverter valve).
Part involved: Current difference of the individual phases on the compressor too high; Vitocal 300-G/333-G: Current difference of the individual phases on the compressor too …; Current difference of power factor correction filter too high (> 10 A); Solar module sensor 10.
When it shows: Type "Note" (H) - triggers "07 Refrigerant circuit" on the heat pump control unit. Heat pump characteristics: Compressor OFF No switching of the appliance connected at plug sS of the solar control module, type SM1 (circulation pump or 3-way diverter valve).
Likely causes:
- Current difference of the individual phases on the compressor too high.
- Vitocal 300-G/333-G: Current difference of the individual phases on the compressor too high.
- Current difference of power factor correction filter too high (> 10 A).
- Lead break, temperature sensor aÖ at solar control module, type SM1.
Is it safe?
| Does the heat pump stop? | Yes |
|---|---|
| Severity | Warning |
| Engineer needed? | Yes |
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.
- Note the 2-character message code and message text shown on the Vitotronic 200 display (press OK for details) and give them to your heating contractor (operating instructions 5817913 p.56).
- You may acknowledge the message once with OK as described in the Vitotronic 200 operating instructions; if it reappears, do not keep acknowledging it - call your contractor.
- Check the heating system pressure gauge reading and report a low reading to your contractor; make sure the filling loop is closed.
What the engineer will check
- Check connecting cable from inverter compressor: See "Connection and ― wiring diagram". ! Please note 400 V appliances: An incorrect rotating field will irreparably damage ….
- Check connecting cable from inverter — compressor. Replace the connecting cable if necessary: See "Connection and wiring diagram". ! Please note 400 V appliances: An ….
- Replace inverter.
- Check sensor aÖ on solar control module, type SM1: See installation and service instructions for solar control module, type SM1.
Who to ask for: Viessmann-trained heat pump engineer with F-gas refrigeration certification; Viessmann-trained heat pump installer/service engineer.
Certification: F-gas certificate (UK F-gas Regulations; Viessmann: refrigerant work by authorised refrigeration engineers only).
What you might notice
Sources
- Service instructions Vitotronic 200 type WO1C heat pump control unit (air/water split & monobloc, brine/water) (6150133, 2023-07) ↗ · 6150133 VSA00004 · pages 171, 177, 165, 185, 97 · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026