S.581 on a Vaillant aroTHERM plus: Connection fault: Frequency converter not recognised Missing communication between the frequency converter and the outdoor unit's PCB. After this occurs three times, fault message F.753 appears
Short answer
On a Vaillant heat pump, S.581 means: Connection fault: Frequency converter not recognised Missing communication between the frequency converter and the outdoor unit's PCB. After this occurs three times, fault message F.753 appears. The heat pump keeps running with some functions stopped.
Reviewed 23 September 2026 · 1 source
What it means
The manual says: Connection fault: Frequency converter not recognised Missing communication between the frequency converter and the outdoor unit's PCB. After this occurs three times, fault message F.753 appears.
Part involved: Heat pump control (status/Live Monitor).
When it shows: Connection fault: Frequency converter not recognised Missing communication between the frequency converter and the outdoor unit's PCB. After this occurs three times, fault message F.753 appears.
Likely causes:
- Connection fault: Frequency converter not recognised Missing communication between the frequency converter and the outdoor unit's PCB. After this occurs three times, fault message F.753 appears.
Is it safe?
| Does the heat pump stop? | Partly |
|---|---|
| Severity | Warning |
The heat pump keeps running with some functions stopped.
Resetting itself: yes - status changes automatically with operating state.
Manual reset: not applicable.
What you can check
- Note the status code (Live Monitor). The heat pump will normally retry automatically; if a related F-code appears or heating/hot water stops, contact your installer.
What the engineer will check
- Read Live Monitor status and fault history; if the status persists or precedes an F-code, follow the corresponding F-code diagnostics in the installer fault table.
Who to ask for: Vaillant-trained heat pump installer/engineer (MCS-certified installer).
Certification: MCS installer certification; Vaillant product training recommended.
What you might notice
What owners and engineers report
8 owner and engineer reports mention this.
- Keeps stopping / cutting out on the aroTHERM plus (VWL ../6 A): 6 reports
- Intermittent fault on the aroTHERM plus (VWL ../6 A): 2 reports
Sources
- Heat pump control interface module (VWZ AI) operating and installation instructions ↗ · 0020291573_01 · page VWZ AI appliance interface 0020291573_01 p.33; uniTOWER VIH QW 190/6 E 0020291525_05 p.58; VWZ MEH 97/6 hydraulic station 0020291544_03 p.51; aroTHERM split hydraulic station VWL ../5 IS 0020257319_05 p.56 · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026