F.1179 on a Viessmann One Base: Internal safety shutdown, inverter, due to mains side phase fault
Short answer
On a Viessmann heat pump, F.1179 means: Internal safety shutdown, inverter, due to mains side phase fault. The heat pump keeps running with some functions stopped. An engineer is needed to fix the cause.
Reviewed 23 September 2026 · 1 source
What it means
The manual says: Internal safety shutdown, inverter, due to mains side phase fault.
Part involved: Internal safety shutdown, inverter, due to mains side phase fault.
When it shows: System characteristics:; Output demand to heat pump not possible; Compressor not available.
Likely causes:
- Failure of one phase for voltage in the inverter intermediate circuit; sharp rise in this voltage.
Is it safe?
| Does the heat pump stop? | Partly |
|---|---|
| Engineer needed? | Yes |
The heat pump keeps running with some functions stopped.
Resetting itself: Not stated per code in Viessmann document 6199893 GB 01/2026 (VSA00009).
Manual reset: User may acknowledge via HMI after noting the code (6249162 p.57); the message returns if the cause persists.
What you can check
- On the HMI, tap the message and "?" to read the system characteristics and Viessmann's user tips; note the code (e.g. F.xxx) and text for your contractor (operating instructions 6249162 p.57).
- Acknowledge the message once via the HMI; do not acknowledge fault messages several times in quick succession (6249162 p.58) - notify your contractor.
- Check the heat pump breaker/isolator in the consumer unit is ON (do not repeatedly reset a breaker or RCD that keeps tripping).
What the engineer will check
- Check the fuse protection for the mains connection of the outdoor unit. Replace fuse if necessary. Note If the power supply was interrupted by the ….
- Check the power supply to X1 of the EMCF filter module of the inverter.
- Check the cable and connections to the inverter:.
- Check wires and plugs for correct seating.
- Check connections for contact corrosion.
- Check cables for mechanical damage, e.g. crushing, kinking, chafing or breakage. Replace the cables if necessary.
- Isolate the outdoor unit from the power supply. Wait at least 2 min. Switch on voltage again.
- Replace inverter.
Who to ask for: Viessmann-trained heat pump engineer / qualified electrician.
Certification: Qualified electrician for work on electrical equipment (Viessmann safety instructions).
What you might notice
Sources
- Service instructions for contractors: Heat pumps in monoblock design incl. hybrid – System configuration and diagnostics (Vitocal 150-A/151-A/250-A/252-A, IDU-A, AWMOF-151/251, AquaSnap 30AWH, BI-BLOC R290) (6199893 GB 01/2026) ↗ · 6199893 GB 01/2026 (VSA00009) · page 187-188 · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026