DEFROST-MIN on a Heliotherm Basic Comfort air split: Heating-side inlet temperature too low during defrost (error messages "H.outH.in Dif." / "Defrost min.")
Short answer
On a Heliotherm heat pump, DEFROST-MIN means: Heating-side inlet temperature too low during defrost (error messages "H.outH.in Dif." / "Defrost min."). The heat pump stops until the fault clears or is reset. An engineer is needed to fix the cause.
Reviewed 23 September 2026 · 1 source
What it means
The manual says: Heating-side inlet temperature too low during defrost (error messages "H.outH.in Dif." / "Defrost min.").
Part involved: Defrost min / H.outH.in Dif.
Likely causes:
- Heat inlet temperature on heating side too low.
Is it safe?
Switch the heat pump off at its isolator and call an engineer.
| Does the heat pump stop? | Yes |
|---|---|
| Severity | Fault — needs a manual reset once the cause is fixed |
| Engineer needed? | Yes |
The heat pump stops until the fault clears or is reset.
Manual reset: Fault clearance function in the controller main menu (web control 321 manual p.27, intended for the Heliotherm competence partner).
What you can check
- Note the error text shown on the controller and contact your Heliotherm competence partner (manual: the heat pump should be shut off and checked by a trained specialist).
- Check the outdoor evaporator is not blocked by leaves, snow or debris.
What the engineer will check
- Increase heating system/buffer temperature.
- Activate 2nd step (backup).
Who to ask for: heat pump / refrigeration (Heliotherm competence partner).
What you might notice
Sources
- Heliotherm Installation Instructions Air Split Heat Pump Basic Comfort Series (Version 1.0, 28.03.2019) - via ManualsLib 3389544 ↗ · Version 1.0 · page 34 · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026