275 on a NIBE heat pump: Compressor phase overloaded long time: Load monitor has prevented the compressor operating at desired power for a long time [other NIBE documents: Load monitor prevents compressor running at desired power]
Short answer
On a NIBE heat pump, 275 means: Compressor phase overloaded long time: Load monitor has prevented the compressor operating at desired power for a long time [other NIBE documents: Load monitor prevents compressor running at desired power]. The heat pump keeps running.
Reviewed 23 September 2026 · 1 source
What it means
The manuals for this range word it in different ways:
- Compressor phase overloaded long time: Load monitor has prevented the compressor operating at desired power for a long time [other NIBE documents: Load monitor prevents compressor running at desired power].
- Com. error slave 5: Temporarily no communication with slave heat pump (EB105).
Part involved: inverter and compressor drive; PCB / accessory board communication.
When it shows: Load monitor has prevented the compressor operating at desired power for a long time; Load monitor prevents compressor running at desired power Temporarily no communication with slave heat pump (EB105).
Likely causes:
- Main fuse too small.
Is it safe?
| Does the heat pump stop? | No |
|---|---|
| Severity | Warning |
The heat pump keeps running.
Resetting itself: yes - None.
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 heat pump and indoor unit breakers/RCD at the consumer unit are on; if one trips again, leave it off and call an engineer.
- 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 breakers for the heat pump, indoor module and any accessories are on at the consumer unit.
What the engineer will check
- 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: Main fuse too small.
- Check communication cables and connectors between PCBs/accessory boards, DIP-switch addressing, power supply to the accessory board, and that accessories activated in the menu are actually fitted.
Who to ask for: NIBE-trained heat pump engineer and/or qualified electrician; NIBE-trained heat pump installer (NIBE PRO / VIP).
Certification: Electrical work to BS 7671 by a competent electrician (notifiable work under Part P in England & Wales); Electrical work to BS 7671 by a competent person.
What you might notice
Sources
- TECHNICAL INFORMATION - ALARM LIST SMO 40 (TIF EN 2042-1, M12658EN) ↗ · TIF EN 2042-1 M12658EN · page 17 · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026