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Heat pumps · Error codes · NIBE
238NIBE · NIBE, all models

238 on a NIBE heat pump: Sensor fault AZ2-BT26: Sensor not connected/defective (brine collector in, FLM 2)

Short answer

On a NIBE heat pump, 238 means: Sensor fault AZ2-BT26: Sensor not connected/defective (brine collector in, FLM 2). The heat pump keeps running with some functions stopped. An engineer is needed to fix the cause.

Reviewed 23 September 2026 · 2 sources

What it means

The manuals for this range word it in different ways:

  • Sensor fault AZ2-BT26: Sensor not connected/defective (brine collector in, FLM 2).
  • High discharge: 3 repeated alarms for high discharge within 4 hours [other NIBE documents: High temperature on discharge sensor BT14, 2 times within 60 minutes or at 115 C or higher for 60 minutes / Temperature deviation on hot gas sensor (Tho-D) twice within 60 min or 60 min continuously].

Part involved: temperature/pressure sensor; compressor discharge (hot gas).

When it shows: Sensor not connected/defective (brine collector in, FLM 2) 3 repeated alarms for high discharge within 4 hours; High temperature on discharge sensor BT14, 2 times within 60 minutes or at 115 C or higher for 60 minutes; Temperature deviation on hot gas sensor (Tho-D) twice within 60 min or 60 min continuously; Heat pump (selected outdoor unit) sends fault message to controller.

Likely causes:

  • S2125: Disruption in the refrigerant circuit; lack of refrigerant | F2120: Disruption in the refrigerant circuit; lack of refrigerant | S2060: Disruption in refrigerant circuit; lack of refrigerant | F2050: Sensor not working; insufficient air circulation or blocked heat exchanger; in cooling possibly insufficient refrigerant; defective PWB1.

Is it safe?

Does the heat pump stop?Partly
SeverityFault — needs a manual reset once the cause is fixed
Engineer needed?Yes

The heat pump keeps running with some functions stopped.

Resetting itself: no/unknown - Circulation pump in FLM blocked.

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.
  • 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 sensor and its connections/wiring against the wiring diagram; measure sensor resistance against the NIBE temperature/resistance table; check the relevant PCB input.
  • Check discharge sensor BT14 mounting, refrigerant charge and circuit (F-gas qualified), airflow over evaporator and heating medium flow. NIBE lists: Disruption in the refrigerant circuit; lack of refrigerant; Disruption in refrigerant circuit; lack of refrigerant; Sensor not working; insufficient air circulation or blocked heat exchanger; in cooling possibly insufficient refrigerant; defective PWB1.

Who to ask for: NIBE-trained heat pump installer (NIBE PRO / VIP); Heat pump engineer with F-gas qualification (NIBE-trained / NIBE PRO installer).

Certification: Electrical work to BS 7671 by a competent person; F-gas certification for refrigerant circuit work (plus flammable-refrigerant competence for R290/R32 models).

What you might notice

Sources

A code explains what the controller detected, not a confirmed root cause.

Reviewed: 23 September 2026