I.81 on a Viessmann One Base: Derating due to excessive temperature of internal power module of inverter
Short answer
On a Viessmann heat pump, I.81 means: Derating due to excessive temperature of internal power module of inverter. 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: Derating due to excessive temperature of internal power module of inverter.
Part involved: Derating due to excessive temperature of internal power module of inverter.
When it shows: System characteristics: Output reduction (derating) by inverter if temperature at internal power module is too high.
Likely causes:
- Output reduction (derating) by inverter if temperature at internal power module is too high.
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.
- 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 for sufficient airflow to cool the inverter.
- Check inverter heat sink and fan for dirt. Carry out cleaning if necessary.
- Check whether the temperature at the inverter temperature sensor is too high, e.g. due to high solar radiation.
Who to ask for: Viessmann-trained heat pump engineer / qualified electrician.
Certification: Qualified electrician for work on electrical equipment (Viessmann safety instructions).
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 219 · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026