REFRIGERANT-LOW on a Stiebel Eltron WPM 3 heat pump manager: Unexpectedly high deviation of expansion valve opening from the pre-control characteristic (superheating high with valve opening above limit)
Short answer
On a Stiebel Eltron heat pump, REFRIGERANT-LOW means: Unexpectedly high deviation of expansion valve opening from the pre-control characteristic (superheating high with valve opening above limit). 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: Unexpectedly high deviation of expansion valve opening from the pre-control characteristic (superheating high with valve opening above limit).
Part involved: compressor / expansion valve / pressure switches.
When it shows: Unexpectedly high deviation of expansion valve opening from the pre-control characteristic (superheating high with valve opening above limit).
Likely causes:
- Refrigerant leak; expansion valve not functioning correctly.
Is it safe?
| Does the heat pump stop? | Yes |
|---|---|
| Severity | Fault — clears by itself when the condition goes |
| Engineer needed? | Yes |
The heat pump stops until the fault clears or is reset.
Resetting itself: yes - restarts after IWS fault time/idle time.
Manual reset: after 5 faults in 2 h run: IWS reset.
What you can check
- Read and note the full message code and time from the WPM display (DIAGNOSIS / NOTIFICATIONLIST if accessible without a code).
- Check the heat pump and controller circuit breakers/isolators at the consumer unit are on.
- Check the outdoor unit air intake/discharge is not blocked by leaves, snow or ice (air source units).
What the engineer will check
- Refrigerant leak; expansion valve not functioning correctly.
Who to ask for: F-gas/refrigeration-qualified heat pump engineer (R290/A3 flammable-refrigerant competence for R290 models).
Certification: F-gas certification for fluorinated refrigerants (R410A/R454C); flammable refrigerant (R290) handling training for R290 models.
What you might notice
Sources
- OPERATION AND INSTALLATION Heat pump manager WPM 3 (DM0000035521) ↗ · A 316199-43934-9674 · page 46, 47, 50 · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026