261 on a NIBE heat pump: High heat exchanger temperature (generated by heat pump): Temperature deviation on the heat exchanger sensor (Tho-R1/R2) five times within 60 minutes or continuously for 60 minutes [other NIBE documents: Temperature deviation on heat exchanger sensor (Tho-R1/R2) 5 times within 60 min or continuously 60 min / High pressure and/or temperature in the evaporator]
Short answer
On a NIBE heat pump, 261 means: High heat exchanger temperature (generated by heat pump): Temperature deviation on the heat exchanger sensor (Tho-R1/R2) five times within 60 minutes or continuously for 60 minutes [other NIBE documents: Temperature deviation on heat exchanger sensor (Tho-R1/R2) 5 times within 60 min or continuously 60 min / High pressure and/or temperature in the evaporator]. 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:
- High heat exchanger temperature (generated by heat pump): Temperature deviation on the heat exchanger sensor (Tho-R1/R2) five times within 60 minutes or continuously for 60 minutes [other NIBE documents: Temperature deviation on heat exchanger sensor (Tho-R1/R2) 5 times within 60 min or continuously 60 min / High pressure and/or temperature in the evaporator].
- Warm outd air, heat. mode: Outside temperature too high to ensure safe operation [other NIBE documents: Temperature of BT28 above the value that permits operation / EB101 sends message to controller].
Part involved: pressure switches/sensors, expansion valve; operating range / outdoor sensor.
When it shows: Temperature deviation on the heat exchanger sensor (Tho-R1/R2) five times within 60 minutes or continuously for 60 minutes; Temperature deviation on heat exchanger sensor (Tho-R1/R2) 5 times within 60 min or continuously 60 min; High pressure and/or temperature in the evaporator; Temperature deviation on heat exchanger sensor (Tho-R1/R2) five times within 60 min or 60 min continuously Outside temperature too high to ensure safe operation; Temperature of BT28 above the value that permits operation; EB101 sends message to controller.
Likely causes:
- S2060: Sensor not working; insufficient air circulation or blocked heat exchanger; defective control board; too much refrigerant | F2050: Sensor not working; insufficient air circulation or blocked heat exchanger; defective PWB1; too much refrigerant | F2040: Sensor not working; insufficient air circulation or blocked heat exchanger; defective control board; too much refrigerant.
- S2060: Warm weather conditions; sensor fault | F2050: Warm weather conditions; sensor fault.
Is it safe?
| Does the heat pump stop? | Partly |
|---|---|
| Severity | Safety lockout |
| Engineer needed? | Yes |
The heat pump keeps running with some functions stopped.
Resetting itself: no/unknown - Compressor 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. Air source systems: check the outdoor unit is clear of leaves/snow/ice. Read the heating system pressure gauge and note the reading for your installer.
- 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. Normally clears by itself when the outdoor temperature returns to the unit's operating range; check the outdoor unit is not buried in snow.
What the engineer will check
- Check heating medium flow, particle filter and circulation pump; check pressure switches/sensors, expansion valve, service valves and refrigerant charge (F-gas qualified). NIBE lists: Defective sensor; insufficient air circulation or blocked heat exchanger; defective control board in F2040/AMS; too much refrigerant; Sensor not working; insufficient air circulation or blocked heat exchanger; defective control board; too much refrigerant; Sensor not working; insufficient air circulation or blocked heat exchanger; defective PWB1; too much refrigerant.
- Check outdoor ambient sensor BT28/Tho-A value and connection; confirm installation is within operating range. NIBE lists: Warm weather conditions; sensor fault.
Who to ask for: Heat pump engineer with F-gas qualification (NIBE-trained / NIBE PRO installer); NIBE-trained heat pump installer (NIBE PRO / VIP).
Certification: F-gas certification for refrigerant circuit work (plus flammable-refrigerant competence for R290/R32 models); None specific beyond competent heat pump installer; electrical work to BS 7671.
What you might notice
Sources
- TECHNICAL INFORMATION - ALARM LIST SMO 40 (TIF EN 2042-1, M12658EN) ↗ · TIF EN 2042-1 M12658EN · page 6 · 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