F.1324 on a Viessmann One Base: Function check: Fault, instantaneous heating water heater
Short answer
On a Viessmann heat pump, F.1324 means: Function check: Fault, instantaneous heating water heater. 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: Function check: Fault, instantaneous heating water heater.
Part involved: Function check: Fault, instantaneous heating water heater.
When it shows: System characteristics: Actuator test active.
Likely causes:
- Limited or no function of the instantaneous heating water heater.
- The function check has detected a fault in the instantaneous heating water heater.
Is it safe?
| Does the heat pump stop? | Not stated |
|---|---|
| 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 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
- Check the following connections:.
- Wall mounted indoor unit: 230 V~ junction box, terminals 136.1 to 136.N3 Floorstanding indoor unit: 230 V~/400 V~ terminal area, lower luster terminal, terminals 136.L1 ….
- Relays K3, K5 and K7 on the EHCU electronics module.
- High limit safety cut-out.
- Instantaneous heating water heater.
- 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 the cables if necessary.
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 199-200 · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026