LOW-PRESSURE on a Stiebel Eltron WPM 3 heat pump manager: The low pressure sensor/minimum low pressure limiter has responded (switching point depends on HP type, e.g. 1.2 bar abs within 60 s for type 1; <2 bar for 10 s type 3; <1.0 bar for 240 s type 4)
Short answer
On a Stiebel Eltron heat pump, LOW-PRESSURE means: The low pressure sensor/minimum low pressure limiter has responded (switching point depends on HP type, e.g. 1.2 bar abs within 60 s for type 1; <2 bar for 10 s type 3; <1.0 bar for 240 s type 4). 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: The low pressure sensor/minimum low pressure limiter has responded (switching point depends on HP type, e.g. 1.2 bar abs within 60 s for type 1; <2 bar for 10 s type 3; <1.0 bar for 240 s type 4).
Part involved: compressor / expansion valve / pressure switches.
When it shows: The low pressure sensor/minimum low pressure limiter has responded (switching point depends on HP type, e.g. 1.2 bar abs within 60 s for type 1; <2 bar for 10 s type 3; <1.0 bar for 240 s type 4).
Likely causes:
- Refrigerant leak/escaped; expansion valve does not open; (type 4) check fan and fuse.
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/escaped; expansion valve does not open; (type 4) check fan and fuse.
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