CONNECTION-FAULT-HEAT-PUMP on a Vaillant aroTHERM: Connection fault: Heat pump
Short answer
On a Vaillant heat pump, CONNECTION-FAULT-HEAT-PUMP means: Connection fault: Heat pump. 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: Connection fault: Heat pump.
Part involved: VWZ AI interface / eBUS.
Likely causes:
- The eBUS connection between the heat pump and the VWZ AI heat pump control interface module is defective.
Is it safe?
| Does the heat pump stop? | Yes |
|---|---|
| Severity | Fault — needs a manual reset once the cause is fixed |
| Engineer needed? | Yes |
The heat pump stops until the fault clears or is reset.
Resetting itself: no - the fault remains displayed until the cause is eliminated.
Manual reset: yes - after the cause is eliminated, press the reset button (indoor unit) or reset via the system control; if it recurs after several resets contact customer service.
What you can check
- Note the full code and text shown on the display (and the date/time it appeared). Check the heat pump supply breaker/isolator (and back-up heater breaker, if separate) at the consumer unit is on; if a breaker has tripped more than once, leave it off and call an engineer - do not open any casing. Do not keep resetting the unit; report the code to your installer (the operating instructions for this product were not checked for a homeowner reset procedure).
What the engineer will check
- Check display-to-main-PCB connection in VWZ AI; check eBUS cable, polarity and supply between heat pump and VWZ AI.
Who to ask for: Heat pump/controls installer familiar with Vaillant eBUS controls.
Certification: MCS installer certification; Vaillant product training recommended.
What you might notice
What owners and engineers report
2 owner and engineer reports mention this.
- No heating on the aroTHERM: 2 reports
Sources
- Installation instructions aroTHERM VWL 55/3 A 230 V, VWL 85/3 A 230 V (GB) ↗ · 0020217827_03 · page VWL ../3 A 0020217827_03 p.34; VWL ../2 A 0020147164_09 p.36 · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026