F.876 on a Viessmann One Base: Lead break, combined sensor, flow rate/temperature
Short answer
On a Viessmann heat pump, F.876 means: Lead break, combined sensor, flow rate/temperature. 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: Lead break, combined sensor, flow rate/temperature.
Part involved: Lead break, combined sensor, flow rate/temperature.
When it shows: System characteristics: Heat pump off.
Likely causes:
- Only for heat pumps with integral flow sensor: Lead break, flow sensor.
Is it safe?
| Does the heat pump stop? | Yes |
|---|---|
| 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).
- Check the system pressure shown on the HMI "System overview" (6249162 p.35) or pressure gauge and report a low reading; make sure the filling loop is closed.
What the engineer will check
- Only for heat pumps with integral flow sensor:.
- Check flow sensor and connections X19.1 to X19.4 on the EHCU electronics module:.
- Check wires and plugs for correct seating.
- Check connections for contact corrosion.
- Check cables for mechanical damage, e.g. crushing, kinking, chafing or breakage.
- Check voltage U between X19.2 and X19.4 on EHCU electronics module:.
- U = 5 V : Replace flow sensor.
- No voltage: Replace EHCU electronics module.
Who to ask for: Viessmann-trained heat pump installer/service engineer.
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 154-155 · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026