E801 on a Viessmann Vitocal 100-A: Pressure inverter timeout (blocks: Compressor)
Short answer
On a Viessmann heat pump, E801 means: Pressure inverter timeout (blocks: Compressor). 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: Pressure inverter timeout (blocks: Compressor).
Part involved: Pressure inverter timeout.
When it shows: When the machine’s controller does not communicate with the driver board of the compressor, a timeout alarm is triggered to avoid losing control of the system.
Likely causes:
- When the machine’s controller does not communicate with the driver board of the compressor, a timeout alarm is triggered to avoid losing control of the ….
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.
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
- Inverter fault: check inverter/compressor driver per Viessmann service documentation; E801 = no communication between controller and compressor driver board.
- Read alarm log (Hist) on controller; contact Viessmann technical assistance if alarm persists.
Who to ask for: Viessmann-trained heat pump engineer / qualified electrician.
Certification: Qualified electrician for work on electrical equipment (Viessmann safety instructions).
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.13.6 printed p.34-35 · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026