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Heat pumps · Error codes · NIBE
742NIBE · NIBE, all models

742 on a NIBE heat pump: Sens flt BP9 outd air ht pump: Sensor fault BP9 (high pressure sensor)

Short answer

On a NIBE heat pump, 742 means: Sens flt BP9 outd air ht pump: Sensor fault BP9 (high pressure sensor). The manual does not say whether the heat pump stops. An engineer is needed to fix the cause.

Reviewed 23 September 2026 · 1 source

What it means

The manual says: Sens flt BP9 outd air ht pump: Sensor fault BP9 (high pressure sensor).

Part involved: temperature/pressure sensor.

When it shows: Sensor fault BP9 (high pressure sensor).

Likely causes:

  • S2125: Open circuit or short circuit on sensor input.

Is it safe?

Does the heat pump stop?Not stated
Engineer needed?Yes

The manual does not say whether the heat pump stops.

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.

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: Open circuit or short circuit on sensor input.

Who to ask for: NIBE-trained heat pump installer (NIBE PRO / VIP).

Certification: Electrical work to BS 7671 by a competent person.

Sources

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

Reviewed: 23 September 2026