94 on a Vaillant geoTHERM: Phase loss - check circuit breaker (one or more phases dropped out)
Short answer
On a Vaillant heat pump, 94 means: Phase loss - check circuit breaker (one or more phases dropped out). 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: Phase loss - check circuit breaker (one or more phases dropped out).
Part involved: Phase loss - check circuit breaker.
When it shows: Fault-induced shutdown: heat pump shut down until the error is reset (Menu I1).
Likely causes:
- Loss of a phase or tripped circuit breaker; badly tightened connections; mains voltage too low; power company block with incorrect E-plan setting; start-up current limiter defective/incorrectly connected.
- Emergency mode (electric auxiliary heating): possible.
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.
Manual reset: yes - by the engineer, by resetting the error in Menu I1 (error history) after removing the cause; emergency mode via the electric auxiliary heater can be enabled where marked.
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. 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 circuit breakers and compressor supply connections; measure voltage; check E-plan setting; check start-up current limiter.
Who to ask for: Heat pump engineer with electrical competence (qualified electrician for supply/phase faults).
Certification: Competent electrician (BS 7671 / Part P) for supply-side work.
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/VWW (GB 07/2008) ↗ · 0020057444_01 · page geoTHERM VWS/VWW 6-17 kW 400 V 0020057444_01 p.74; geoTHERM VWS/VWW 22-46 kW 0020051574_04 p.106 · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026