152 on a NIBE heat pump: Sen flt: CL12-BT51 pool temperature sensor: Sensor input unreasonable value for longer than 5 s
Short answer
On a NIBE heat pump, 152 means: Sen flt: CL12-BT51 pool temperature sensor: Sensor input unreasonable value for longer than 5 s. The heat pump keeps running with some functions stopped.
Reviewed 23 September 2026 · 1 source
What it means
The manual says: Sen flt: CL12-BT51 pool temperature sensor: Sensor input unreasonable value for longer than 5 s.
Part involved: temperature/pressure sensor.
When it shows: Sensor input unreasonable value for longer than 5 s.
Likely causes:
- Sensor not connected; open-circuit or defective sensor.
Is it safe?
| Does the heat pump stop? | Partly |
|---|---|
| Severity | Warning |
The heat pump keeps running with some functions stopped.
Resetting itself: yes - Pool pump stops.
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.
What the engineer will check
- Check sensor and its connections/wiring against the wiring diagram; measure sensor resistance against the NIBE temperature/resistance table; check the relevant PCB input. NIBE lists: Sensor not connected; open-circuit or defective sensor.
Who to ask for: NIBE-trained heat pump installer (NIBE PRO / VIP).
Certification: Electrical work to BS 7671 by a competent person.
Sources
- TECHNICAL INFORMATION - ALARM LIST SMO 40 (TIF EN 2042-1, M12658EN) ↗ · TIF EN 2042-1 M12658EN · page 14 · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026