NIBE
The NIBE S2125-8 is a 5.33 kW monobloc air-source heat pump with an A+++ ErP rating at 35°C and a SCOP of 5.0, capable of delivering 75°C flow temperature.
The NIBE S2125-8 is an air-source monobloc heat pump designed for domestic heating applications in the UK. This page provides detailed technical specifications, performance data, fault codes, and compatibility information for heating engineers and homeowners. Manufactured in Sweden, the S2125-8 is part of the NIBE S2125 product family, offering a compact and efficient solution for modern heating systems.
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Full technical specifications extracted from the manufacturer brochure. Empty sections are hidden.
The NIBE S2125-8 is a 5.33 kW nominal capacity inverter-driven monobloc air-source heat pump, utilising R290 refrigerant with a low GWP of 3. It achieves a Seasonal Coefficient of Performance (SCOP) of 5.0 at 35°C and 3.7 at 55°C, earning an ErP rating of A+++ at 35°C and A++ at 55°C. The unit can deliver a maximum flow temperature of 75°C and operates down to an outdoor temperature of -25°C. Installation requires a minimum water flow rate of 19.2 litres per minute and a buffer tank. The outdoor unit measures 1080mm (H) x 1128mm (W) x 831mm (D) and weighs 163 kg. Standard warranty is two years, covering parts and labour, subject to registration.
Every fault code listed in the manufacturer brochure, with likely causes and engineer actions. Each code has a permalink — paste a URL like https://www.boilertag.com/heat-pumps/nibe/s2125-8#fault-156 (80) to jump straight to the entry.
| Code | Meaning | Details |
|---|---|---|
| 156 (80) | Low Ip cooling Show causes & actions5 repeated alarms for low low-pressure within 4 hours. Likely causes
| Details |
| 224 (182) | Fan alarm from heat pump Show causes & actions5 unsuccessful start attempt. Likely causes
| Details |
| 225 (8) | Exchange Sensors flow/return Show causes & actionsReturn is hotter than flow. Likely causes
| Details |
| 228 (2) | Unsuccessful defrosting Show causes & actions10 failed consecutive defrostings. Likely causes
| Details |
| 229 (4) | Short run times for compressor Show causes & actionsOperation is stopped from the indoor section after less than 5 minutes. Likely causes
| Details |
| 230 (78) | Hot gas alarm Show causes & actions3 repeated alarms for high discharge within 4 hours. Likely causes
| Details |
| 232 (76) | Low evaporation temp Show causes & actions5 repeated alarms for low evaporation temperature within 4 hours. Likely causes
| Details |
| 264 (203) | Communication fault to Inverter Show causes & actionsAlarm 203 from heat pump for 20 seconds. Likely causes
| Details |
| 298 (92) | Fault in inverter. Heating not working. Show causes & actionsThe inverter has tried to heat up the compressor, but has failed. Likely causes
| Details |
| 300 (94) | Sensor BT14 or BP9 loose or defective Show causes & actionsSensor BT14 or BP9 has come loose or is otherwise defective. Likely causes
| Details |
| 341 (6) | Recurring safety defr. Show causes & actions10 repeated defrostings according to the protection conditions. Likely causes
| Details |
| 344 (72) | Recurring low pressure Show causes & actions5 repeated low pressure alarm within 4 hours. Likely causes
| Details |
| 346 (74) | Recurring high pressure Show causes & actions5 repeated high pressure alarm within 4 hours. Likely causes
| Details |
| 400 (207) | Unspecified faults Show causes & actionsInitiation fault, inverter. Likely causes
| Details |
| 400 (209) | Unspecified faults Show causes & actionsThe inverter is not compatible | Details |
| 400 (211) | Unspecified faults Show causes & actionsConfiguration file missing. | Details |
| 400 (213) | Unspecified faults Show causes & actionsCharge error configuration. | Details |
| 425 (108) | Persistent pressure switch or over-temperature alarm. Show causes & actions2 repeated LP/HP/FQ alarms within 2.5 hours. Likely causes
| Details |
| 427 (110) | Safety stop, inverter Show causes & actionsTemporary fault in inverter, 2 times within 60 minutes. Likely causes
| Details |
| 429 (112) | Safety stop, inverter Show causes & actionsTemporary fault in inverter, 3 times within 2 hours. Likely causes
| Details |
| 437 (120) | Mains disturbance Show causes & actionsTemporary fault in inverter, 3 times within 2 hours or continuously for 1 hour. Likely causes
| Details |
| 439 (122) | Overheated inverter Show causes & actionsThe inverter has temporarily reached max working temperature, due to poor cooling 3 times within 2 hours or continuously for 1 hour. Likely causes
| Details |
| 441 (124) | Current too high Show causes & actionsCurrent to inverter too high, 3 times within 2 hours or continuously for 1 hour. Likely causes
| Details |
| 443 (126) | Overheated inverter Show causes & actionsThe inverter has temporarily reached max working temperature, due to poor cooling 3 times within 2 hours or continuously for 1 hour. Likely causes
| Details |
| 447 (130) | Phase failure Show causes & actionsCompressor phase is missing, 3 times within 2 hours or continuously for 1 minute. Likely causes
| Details |
| 449 (132) | Failed compressor starts Show causes & actionsCompressor does not start when required, 3 times within 2 hours. Likely causes
| Details |
| 453 (136) | High current load, compressor Show causes & actionsThe output current from the inverter to the compressor has been temporarily too high 3 times within 2 hours or continuously for 1 hour. Likely causes
| Details |
| 455 (138) | High power load, compressor Show causes & actionsThe power output from the inverter has been too high 3 times within 2 hours or continuously for 1 hour. Likely causes
| Details |
| 501 (184) | Failed start, no pressure diff. Show causes & actionsThe pressure difference between BP9 and BP8 has been too low at compressor start 3 times within 30 minutes. Likely causes
| Details |
| 503 (186) | Compressor speed too low Show causes & actionsCompressor speed below lowest permitted speed. Likely causes
| Details |
| 523 | Low defrosting flow Show causes & actionsThe flow is low. Check particle filter and pump. Likely causes
| Details |
| 589 (216) | Incorrect PCBA in heat pump. Change to a new PCBA suitable for S2125. Show causes & actionsThe heat pump has the wrong base board. Likely causes
| Details |
| 740 (56) | Sensor fault from heat pump Show causes & actionsSensor fault BT84. Likely causes
| Details |
| 742 (52) | Sensor fault from heat pump Show causes & actionsSensor fault BP9. Likely causes
| Details |
| 744 (50) | Sensor fault from heat pump Show causes & actionsSensor fault BP8. Likely causes
| Details |
| 746 (46) | Sensor fault from heat pump Show causes & actionsSensor fault BT28 Likely causes
| Details |
| 748 (44) | Sensor fault from heat pump Show causes & actionsSensor fault BT17. Likely causes
| Details |
| 750 (34) | Sensor fault from heat pump Show causes & actionsSensor fault BT3. Likely causes
| Details |
| 752 (42) | Sensor fault from heat pump Show causes & actionsSensor fault BT16. Likely causes
| Details |
| 754 (40) | Sensor fault from heat pump Show causes & actionsSensor fault BT15. Likely causes
| Details |
| 756 (38) | Sensor fault from heat pump Show causes & actionsSensor fault BT14. Likely causes
| Details |
| 758 (36) | Sensor fault from heat pump Show causes & actionsSensor fault BT12. Likely causes
| Details |
| 762 (90) | Persistent excess temperature alarm. Show causes & actions2 repeated FQ alarms within 2.5 hours. Likely causes
| Details |
| 765 (88) | Persistent high pressure switch alarm. Show causes & actions2 repeated HP alarms within 2.5 hours. Likely causes
| Details |
| 767 (82) | Persistent low pressure switch alarm. Show causes & actions2 repeated LP alarms within 2.5 hours. Likely causes
| Details |
Patterns that group across the manufacturer's fault-code table. Each entry links to the full code listing further down the page.
Triggered by fault code 156 (80).
Triggered by fault code 224 (182).
Triggered by fault code 225 (8).
Triggered by fault code 228 (2).
Triggered by fault code 229 (4).
Common questions from engineers and homeowners about the NIBE S2125-8.
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Specifications on this page are extracted from the manufacturer brochure. Always cross-check against the latest datasheet before commissioning or quoting. Last updated 28 June 2026.