F.1094 on a Viessmann One Base: No flow rate in the cylinder loading system
Short answer
On a Viessmann heat pump, F.1094 means: No flow rate in the cylinder loading system. 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: No flow rate in the cylinder loading system.
Part involved: No flow rate in the cylinder loading system.
When it shows: System characteristics: No DHW heating.
Likely causes:
- No flow rate in the cylinder loading system.
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 6199961 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
- Isolate the system from the power supply. Wait at least 2 min. Switch on the system.
- Loading cylinder individually: Check the shut-off valves and 3-way valves:.
- If necessary, open closed shut-off valves and 3way valves in the direction of DHW heating.
- Check for leaks.
- Indoor unit individually:.
- Check the non-return valve on the cylinder loading pump, if installed.
- Check the electrical connections and function of the cylinder loading pump. Replace the SLP-ADIO electronics module if necessary.
- Flush thoroughly on the DHW side.
Who to ask for: Viessmann-trained heat pump installer/service engineer.
What you might notice
Sources
- Service instructions: Heat pumps in split design incl. hybrid – System configuration and diagnostics (Vitocal 200-S/222-S One Base) (6199961 GB 01/2026) ↗ · 6199961 VSA00009 · page 172 · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026