355 on a NIBE heat pump: Slave EB101 / failed sensor calibration BT3-BT63: Delta BT3-BT63 larger than 2 K after calibration [other NIBE documents: Delta BT3-BT63 greater than 2 K after calibration]
Short answer
On a NIBE heat pump, 355 means: Slave EB101 / failed sensor calibration BT3-BT63: Delta BT3-BT63 larger than 2 K after calibration [other NIBE documents: Delta BT3-BT63 greater than 2 K after calibration]. 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: Slave EB101 / failed sensor calibration BT3-BT63: Delta BT3-BT63 larger than 2 K after calibration [other NIBE documents: Delta BT3-BT63 greater than 2 K after calibration].
Part involved: temperature/pressure sensor.
When it shows: Delta BT3-BT63 larger than 2 K after calibration; Delta BT3-BT63 greater than 2 K after calibration.
Likely causes:
- Flow-related.
Is it safe?
| Does the heat pump stop? | Not stated |
|---|---|
| Severity | Fault — needs a manual reset once the cause is fixed |
| Engineer needed? | Yes |
The manual does not say whether the heat pump stops.
Resetting itself: no/unknown - Circulation pump changes from auto to manual speed; Changes from auto to manual pump speed.
Manual reset: Reset from the controller alarm menu ('reset alarm' / 'Reset alarm and try again'); alarm recurs if the cause remains - NIBE: Circulation pump changes from auto to manual speed; Changes from auto to manual pump speed.
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: Flow-related.
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 18 · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026