A.70 on a Viessmann One Base: Filter in ball valve of outdoor unit is contaminated
Short answer
On a Viessmann heat pump, A.70 means: Filter in ball valve of outdoor unit is contaminated. 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: Filter in ball valve of outdoor unit is contaminated.
Part involved: Filter in ball valve of outdoor unit is contaminated.
When it shows: System characteristics: Flow rate too low.
Likely causes:
- Filter in ball valve of outdoor unit is contaminated.
Is it safe?
| Does the heat pump stop? | Not stated |
|---|---|
| Severity | Warning |
| Engineer needed? | Yes |
The manual does not say whether the heat pump stops.
Resetting itself: Not stated per code in Viessmann document 6171807 GB 10/2021.
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
- Clean the filter in the outdoor unit ball valve.
Who to ask for: Viessmann-trained heat pump installer/service engineer.
What you might notice
Sources
- Installation and service instructions Vitocal 150-A, AWO(-M)-E-AC/AWO(-M)-E-AC-AF 151.A (6171807, 2021-10) ↗ · 6171807 VSA00001 · page 117 · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026