Heat pumps · Error codes · Kronoterm
Defrost-T-Flow-ALARMKronoterm · TERMOTRONIC-controlled heat pumps (legacy WP / WPL / WPLV water-water, brine-water, air-water)
Defrost-T-Flow-ALARM on a Kronoterm TERMOTRONIC-controlled heat pumps: Return water temperature during defrost too low - HP lacks energy to defrost
Short answer
On a Kronoterm heat pump, Defrost-T-Flow-ALARM means: Return water temperature during defrost too low - HP lacks energy to defrost. 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: Return water temperature during defrost too low - HP lacks energy to defrost.
Part involved: defrost / buffer.
Likely causes:
- Return water temperature during defrost too low.
Is it safe?
| 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: After fixing the cause restart by holding ENTER for 3 s.
What you can check
- Note the exact message shown on the TERMOTRONIC display.
- Switch on the backup heat source from the controller if the manual allows (heat buffer to at least 20 C), then bring heat emitters back one circuit at a time.
What the engineer will check
- Check buffer sizing/backup heater operation.
Who to ask for: heat pump engineer.
What you might notice
Sources
- KRONOTERM Owner's manual for heat pumps water-water, brine-water and air-water (TERMOTRONIC controller), Id 17-16-19-2972-05 ↗ · 17-16-19-2972-05 · page 52, 59 · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026