4 on a Vaillant geoTHERM: XXX address YY sensor fault ZZZ (sensor on an eBUS component)
Short answer
On a Vaillant heat pump, 4 means: XXX address YY sensor fault ZZZ (sensor on an eBUS component). The heat pump keeps running with some functions stopped. An engineer is needed to fix the cause.
Reviewed 23 September 2026 · 1 source
What it means
The manual says: XXX address YY sensor fault ZZZ (sensor on an eBUS component).
Part involved: XXX address YY sensor fault ZZZ.
Likely causes:
- A sensor ZZZ on an eBUS-connected component with address YY is defective.
Is it safe?
| Does the heat pump stop? | Partly |
|---|---|
| Severity | Warning |
| Engineer needed? | Yes |
The heat pump keeps running with some functions stopped.
Resetting itself: yes - clears when the component/sensor is available.
Manual reset: not required.
What you can check
- Note the full code and text shown on the display (and the date/time it appeared). The geoTHERM operating manual says: do not attempt to remove the source of the malfunction yourself; only an expert technician can remedy the fault and reset the error code. Warnings (26, 36) and temporary faults can be noted and discussed at the next inspection.
What the engineer will check
- Check the ProE plugs on the PCBs, check the sensor functions, replace the sensor.
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
1 owner and engineer report mentions this.
- No heating on the geoTHERM (VWS/VWW ../2, VWS ../3): 1 report
Sources
- Installation instructions geoTHERM VWS 6-10kW 230V (GB 08/2008) ↗ · 0020046310_01 · page geoTHERM VWS 6-10 kW 230 V 0020046310_01 p.71; geoTHERM VWS/VWW 6-17 kW 400 V 0020057444_01 p.69; geoTHERM VWS/VWW 22-46 kW 0020051574_04 p.98 · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026