26 on a Vaillant geoTHERM: Overheating on compressor pressure side
Short answer
On a Vaillant heat pump, 26 means: Overheating on compressor pressure side. The heat pump keeps running. An engineer is needed to fix the cause.
Reviewed 23 September 2026 · 1 source
What it means
The manual says: Overheating on compressor pressure side.
Part involved: Overheating on compressor pressure side.
When it shows: Warning message (error memory and Menu 1); no shutdown.
Likely causes:
- Excessively high output with a high flow temperature.
Is it safe?
| Does the heat pump stop? | No |
|---|---|
| Severity | Warning |
| Engineer needed? | Yes |
The heat pump keeps running.
Resetting itself: n/a - warning only; heat pump (incl. compressor) stays in operation.
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
- Reduce the heating curve; check required heating output (e.g. floor drying, building shell) and reduce if necessary.
Who to ask for: F-gas certified refrigeration engineer with heat pump experience (R290 flammable-refrigerant competence required for aroTHERM plus / GeniaAir).
Certification: F-gas Category I (Regulation (EU) 517/2014 as retained in GB) certificate; flammable (R290) refrigerant training for R290 units.
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; geoTHERM exclusive operating manual 0020071929_00 p.26 · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026