617 on a NIBE heat pump: Temperature protection compressor activated: 2 repeated FQ alarms within 2.5 hours
Short answer
On a NIBE heat pump, 617 means: Temperature protection compressor activated: 2 repeated FQ alarms within 2.5 hours. The heat pump keeps running with some functions stopped. An engineer is needed to fix the cause.
Reviewed 23 September 2026 · 1 source
What it means
The manual says: Temperature protection compressor activated: 2 repeated FQ alarms within 2.5 hours.
Part involved: compressor discharge (hot gas).
When it shows: 2 repeated FQ alarms within 2.5 hours.
Likely causes:
- S2125: Poor heating medium flow; lack of refrigerant; S2125-16/-20: FQ14.1 compressor peak 130 C, FQ14.2 compressor intake 75 C.
Is it safe?
| Does the heat pump stop? | Partly |
|---|---|
| Severity | Safety lockout |
| Engineer needed? | Yes |
The heat pump keeps running with some functions stopped.
Resetting itself: no/unknown - not stated.
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 discharge sensor BT14 mounting, refrigerant charge and circuit (F-gas qualified), airflow over evaporator and heating medium flow. NIBE lists: Poor heating medium flow; lack of refrigerant; S2125-16/-20: FQ14.1 compressor peak 130 C, FQ14.2 compressor intake 75 C.
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
- Installer manual Air/water heat pump NIBE S2125 UK 1x230V IHB EN 2525-1 (831874) ↗ · IHB EN 2525-1 · page 43 · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026