252 on a NIBE heat pump: Com. error slave: Temporarily no communication with slave heat pump
Short answer
On a NIBE heat pump, 252 means: Com. error slave: Temporarily no communication with slave heat pump. 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:
- Com. error slave: Temporarily no communication with slave heat pump.
- Power transistor too hot: Protection against damage if current too high [other NIBE documents: IPM displays FO fault output five times during 60 minutes / Overheated power transistor].
Part involved: PCB / accessory board communication; inverter and compressor drive.
When it shows: Temporarily no communication with slave heat pump Protection against damage if current too high; IPM displays FO fault output five times during 60 minutes; Overheated power transistor.
Likely causes:
- S2060: Interference on incoming supply; service valve closed; insufficient refrigerant; compressor fault; defective inverter board QA40 (PWB2) | F2050: 15 V power supply to inverter PCB unstable.
Is it safe?
| Does the heat pump stop? | Partly |
|---|---|
| Severity | Fault — 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 - Compressor in slave 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. Check the breakers for the heat pump, indoor module and any accessories are on at the consumer unit.
- 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 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.
- 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: Interference on incoming supply; service valve closed; insufficient refrigerant; compressor fault; defective inverter board QA40 (PWB2); 15 V power supply to inverter PCB unstable.
Who to ask for: NIBE-trained heat pump installer (NIBE PRO / VIP); NIBE-trained heat pump engineer and/or qualified electrician.
Certification: Electrical work to BS 7671 by a competent person; 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 7 · Reviewed 23 September 2026
- Installer manual Air/water heat pump NIBE S2060 UK 1x230V IHB EN 2623-3 (831281) ↗ · IHB EN 2623-3 · page 31 · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026