AB on a Viessmann Vitotronic 200: Current phase L3 of compressor too high
Short answer
On a Viessmann heat pump, AB means: Current phase L3 of 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 phase L3 of compressor too high.
- Vitocal 300-G/333-G: Current phase L3 of compressor too high.
- Instant.htg wtr heater: Instantaneous heating water heater does not start up.
Part involved: Current phase L3 of compressor too high; Vitocal 300-G/333-G: Current phase L3 of compressor too high; Instant.htg wtr heater.
When it shows: Type "Note" (H) - triggers "07 Refrigerant circuit" on the heat pump control unit. Heat pump characteristics: Compressor OFF Instantaneous heating water heater does not start up.
Likely causes:
- Current phase L3 of compressor too high.
- Vitocal 300-G/333-G: Current phase L3 of compressor too high.
- Instantaneous heating water heater faulty.
- High limit safety cut-out has responded.
- No temperature rise within 24 h.
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
- Test coil resistance at compressor. Resistance on all windings must be similar (±10 %). For mΩ use a suitable measuring device.
- Replace compressor and/or inverter if required.
- Replace compressor and/or inverter if necessary.
- Danger Contact with live components can lead to serious injury from electric current. Isolate the power supply prior to starting work on the appliance.
- Check power supply, connecting cable and plug for the instantaneous heating water heater.
- Check instantaneous heating water heater control signal at terminals 211.3 (stage 1, see "Main PCB") and 224.4 (stage 2, see "Expansion PCB").
- Check high limit safety cut-out, and reset if required.
- Check instantaneous heating water heater.
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, 178, 100-101 · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026