181 on a NIBE heat pump: Failed periodic increase: Periodic hot water increase did not reach stop temperature within 5 hours [other NIBE documents: Periodic hot water increase did not reach stop temperature in 5 hours]
Short answer
On a NIBE heat pump, 181 means: Failed periodic increase: Periodic hot water increase did not reach stop temperature within 5 hours [other NIBE documents: Periodic hot water increase did not reach stop temperature in 5 hours]. The heat pump keeps running.
Reviewed 23 September 2026 · 1 source
What it means
The manuals for this range word it in different ways:
- Failed periodic increase: Periodic hot water increase did not reach stop temperature within 5 hours [other NIBE documents: Periodic hot water increase did not reach stop temperature in 5 hours].
- Non-calibrated air flow sensor: Air flow sensor has not been calibrated.
Part involved: heating medium flow, charge pump, particle filter; fans, air filters, air sensors.
When it shows: Periodic hot water increase did not reach stop temperature within 5 hours; Periodic hot water increase did not reach stop temperature in 5 hours Air flow sensor has not been calibrated.
Likely causes:
- Incorrect settings.
Is it safe?
| Does the heat pump stop? | No |
|---|---|
| Severity | Information only |
The heat pump keeps running.
Resetting itself: yes - Only information.
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. Read the heating system pressure gauge and check that radiator/underfloor thermostats are not all closed; check heating and hot water temperature settings have not been changed.
- 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 exhaust air valves/grilles in the rooms are open and not blocked; check the filter reminder in the user manual maintenance section.
What the engineer will check
- Check heating medium flow (pump speed/settings, particle filter, air in system), heating curve and hot water settings, correct sensor placement and flow/return connections. NIBE lists: Incorrect settings.
- Check ventilation airflow, fans, filters, air sensors and condensate drainage/level monitor.
Who to ask for: NIBE-trained heat pump installer (NIBE PRO / VIP).
Certification: 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 15 · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026