500 on a NIBE heat pump: Failed start, no press. diff: Pressure difference between BP9 and BP8 too low at compressor start [other NIBE documents: Incorrect pressure between BP8 and BP9 at compressor start]
Short answer
On a NIBE heat pump, 500 means: Failed start, no press. diff: Pressure difference between BP9 and BP8 too low at compressor start [other NIBE documents: Incorrect pressure between BP8 and BP9 at compressor start]. The heat pump keeps running.
Reviewed 23 September 2026 · 1 source
What it means
The manual says: Failed start, no press. diff: Pressure difference between BP9 and BP8 too low at compressor start [other NIBE documents: Incorrect pressure between BP8 and BP9 at compressor start].
Part involved: pressure switches/sensors, expansion valve.
When it shows: Pressure difference between BP9 and BP8 too low at compressor start; Incorrect pressure between BP8 and BP9 at compressor start.
Likely causes:
- F2120: Problem in cooling circuit; defective pressure sensors.
Is it safe?
| Does the heat pump stop? | No |
|---|---|
| Severity | Warning |
The heat pump keeps running.
Resetting itself: yes - Compressor does not start.
Manual reset: Reset from the controller alarm menu ('reset alarm' / 'Reset alarm and try again'); alarm recurs if the cause remains.
What you can check
- Read the alarm text and the 'info/action' help on the controller display (VVM/SMO or S-series smartguide). NIBE's manuals let the homeowner select 'reset alarm' ('Reset alarm and try again' on S-series); if the lamp returns to normal the alarm has cleared. If it comes back, do not keep resetting: select 'aid mode' ('Auxiliary operation' on S-series) if offered, so any electric additional heat keeps heat/hot water going, and contact your installer. Air source systems: check the outdoor unit is clear of leaves/snow/ice. Read the heating system pressure gauge and note the reading for your installer.
What the engineer will check
- Check heating medium flow, particle filter and circulation pump; check pressure switches/sensors, expansion valve, service valves and refrigerant charge (F-gas qualified). NIBE lists: Fault in pressure sensor BP8/BP9; compressor not compressing sufficiently; compressor breakdown; Problem in cooling circuit; defective pressure sensors.
Who to ask for: Heat pump engineer with F-gas qualification (NIBE-trained / NIBE PRO installer).
Certification: F-gas certification for refrigerant circuit work (plus flammable-refrigerant competence for R290/R32 models).
What you might notice
Sources
- TECHNICAL INFORMATION - ALARM LIST SMO 40 (TIF EN 2042-1, M12658EN) ↗ · TIF EN 2042-1 M12658EN · page 20 · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026