419 on a NIBE heat pump: Freeze prot. exch. defr.: Frost protection exchanger defrosting

What it means

The manual says: Freeze prot. exch. defr.: Frost protection exchanger defrosting.

Part involved: heating medium flow, charge pump, particle filter.

When it shows: Frost protection exchanger defrosting.

Likely causes:

• Flow-related.

Is it safe?

The heat pump keeps running with some functions stopped.

Resetting itself: yes - Defrosting stopped.

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.

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: Flow-related.

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

• Short cycling
• Insufficient heating (house not warm enough)
• Heating on when not wanted / house too hot

Sources

• TECHNICAL INFORMATION - ALARM LIST SMO 40 (TIF EN 2042-1, M12658EN) ↗ · TIF EN 2042-1 M12658EN · page 18 · Reviewed 23 September 2026

A code explains what the controller detected, not a confirmed root cause.

Reviewed: 23 September 2026