I.179 on a Viessmann One Base: Temporary Modbus communication fault between inverter and refrigerant circuit controller
Short answer
On a Viessmann heat pump, I.179 means: Temporary Modbus communication fault between inverter and refrigerant circuit controller. The manual does not say whether the heat pump stops. An engineer is needed to fix the cause.
Reviewed 23 September 2026 · 1 source
What it means
The manual says: Temporary Modbus communication fault between inverter and refrigerant circuit controller.
Part involved: Temporary Modbus communication fault between inverter and refrigerant circuit controller.
Likely causes:
- Temporary Modbus communication fault between inverter and refrigerant circuit controller.
Is it safe?
| Does the heat pump stop? | Not stated |
|---|---|
| Severity | Information only |
| Engineer needed? | Yes |
The manual does not say whether the heat pump stops.
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.
What the engineer will check
- Suppress electromagnetic interference on the Modbus connections. Check the cable routing between the VCMU refrigerant circuit controller and the inverter. Adjust the cable routing if ….
- Check the Modbus cable between the VCMU refrigerant circuit controller and 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 Modbus cable if necessary.
Who to ask for: Viessmann-trained heat pump engineer with F-gas certification and R290 (A3 flammable refrigerant) competence.
Certification: F-gas certificate (UK F-gas Regulations; EU 2015/2067 Cat. I cited by Viessmann) plus A3/R290 competence per EN 378-4 or IEC 60335-2-40 Annex HH (6202263 p.2).
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 223 · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026