326 on a NIBE heat pump: Fault in EB16: Active defrosting has failed three times in a row
Short answer
On a NIBE heat pump, 326 means: Fault in EB16: Active defrosting has failed three times in a row. The manual does not say whether the heat pump stops. 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:
- Fault in EB16: Active defrosting has failed three times in a row.
- Low mains voltage: Phase voltage to inverter too low, 3 times within 3 hours or continuously for 1 hour [other NIBE documents: Phase voltage to inverter too low, below 180 V for more than 1 hour].
Part involved: evaporator defrost; inverter and compressor drive.
When it shows: Active defrosting has failed three times in a row Phase voltage to inverter too low, 3 times within 3 hours or continuously for 1 hour; Phase voltage to inverter too low, below 180 V for more than 1 hour.
Likely causes:
- F2120: Low supply voltage or phase loss.
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 - Heat pump changes to passive defrost.
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. Check the outdoor unit is not blocked by leaves, snow or ice and that nothing obstructs the airflow.
- 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. Check the heat pump and indoor unit breakers/RCD at the consumer unit are on; if one trips again, leave it off and call an engineer.
What the engineer will check
- Check system volume and flow during defrost, particle filter, circulation pump, evaporator airflow, evaporator/defrost sensors and refrigerant circuit.
- Check main and group fuses and cable connections, supply voltage under load, inverter terminal blocks, inverter mounting/cooling paste, compressor wiring and compressor. NIBE lists: Low supply voltage or phase loss.
Who to ask for: NIBE-trained heat pump installer (NIBE PRO / VIP); NIBE-trained heat pump engineer and/or qualified electrician.
Certification: None specific beyond competent heat pump installer; electrical work to BS 7671; Electrical work to BS 7671 by a competent electrician (notifiable work under Part P in England & Wales).
What you might notice
Sources
- ALARM LIST - NIBE products with Emmy display, Version 1747-1 (updated 2017-11-23) ↗ · 1747-1 · page 9 · Reviewed 23 September 2026
- Installer manual Air/water heat pump NIBE F2120 IHB EN 2214-1 (631982) ↗ · IHB EN 2214-1 · page 38 · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026