F.836 on a Viessmann One Base: Load current of inverter too high (excess current)
Short answer
On a Viessmann heat pump, F.836 means: Load current of inverter too high (excess current). 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 manual says: Load current of inverter too high (excess current).
Part involved: Load current of inverter too high (excess current).
When it shows: System characteristics: Refrigerant circuit off: Inverter and compressor cannot be switched on.
Likely causes:
- Inverter load current too high (excess current):.
- Short circuit between phases.
- Blocked compressor armature.
Is it safe?
| Does the heat pump stop? | Yes |
|---|---|
| Severity | Safety lockout |
| Engineer needed? | Yes |
The heat pump stops until the fault clears or is reset.
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 all connections to the compressor:.
- 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 cable if necessary.
- Check phase connections for compressor for clockwise rotating field.
- Isolate the system from the power supply. Wait at least 2 min. Switch on the system.
- Replace inverter.
- Replace compressor. If necessary, inform the manufacturer's technical support.
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 149 · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026