E020 on a Viessmann Vitocal 100-A: Inverted trasductors pressure alarm (blocks: Machine/san)
Short answer
On a Viessmann heat pump, E020 means: Inverted trasductors pressure alarm (blocks: Machine/san). 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: Inverted trasductors pressure alarm (blocks: Machine/san).
Part involved: Inverted trasductors pressure alarm.
When it shows: For compressor enabled for more than 150 seconds, the suctio n pressure probe detect a pressure higher than the condensation pressure probe, the alarm displayed is E020. The alarm is not resettable (it is necessary to cut the power supply to eliminate the alarm). This ….
Likely causes:
- For compressor enabled for more than 150 seconds, the suctio n pressure probe detect a pressure higher than the condensation pressure probe, the alarm displayed ….
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 resettable - power must be cut (s.13.3).
Manual reset: Placing the controller in OFF mode resets alarms and hour counters (6167577 s.13, printed p.34); if alarms persist when switched on, contact technical assistance.
What you can check
- Note the E-code (e.g. E006) shown on the Vitocal 100-A controller display and give it to your installer.
- Per 6167577 s.13, switching the controller to OFF resets alarms; if the alarm is still present when switched back on, stop and contact your installer/Viessmann technical assistance (do not keep cycling it).
- Check the heat pump breaker/isolator in the consumer unit is ON and the outdoor unit is not blocked by leaves, debris or snow.
What the engineer will check
- Read alarm log (Hist) on controller; contact Viessmann technical assistance if alarm persists.
Who to ask for: Viessmann-trained heat pump engineer with F-gas refrigeration certification.
Certification: F-gas certificate (UK F-gas Regulations; Viessmann: refrigerant work by authorised refrigeration engineers only).
Sources
- Installation/service instructions Vitocal 100-A outdoor unit controller (6167577, 9/2020) ↗ · 6167577 VSA00001 · page 36 (PDF p.38) table 13.2; detail s.13.3 printed p.34-35 · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026