Heat pumps · Error codes · Kronoterm
2335-b4Kronoterm · KSM system controller / KT-2A / Cloud.Kronoterm alarm list (ADAPT, VERSI, ETERA, WPLV, ADAPT MAX)
2335-b4 on a Kronoterm KSM system controller / KT-2A / Cloud.Kronoterm alarm list: AC under voltage fault
Short answer
On a Kronoterm heat pump, 2335-b4 means: AC under voltage fault. 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: AC under voltage fault.
Part involved: power supply.
Likely causes:
- AC under voltage fault.
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.
Resetting itself: Manual note: auto-reset attempted; if still active 10 min after auto-reset contact installer.
Manual reset: User may clear via KT-2A / Cloud.Kronoterm "Confirm"; conditions re-checked.
What you can check
- Note the full code (4-digit number + bit, e.g. 2335-b4) from the KT-2A diagnostic menu or Cloud.Kronoterm alarm list.
- Reset/confirm the alarm once from the KT-2A or Cloud.Kronoterm ("Confirm") as the manual allows; if still active 10 min after the reset, contact the installer who commissioned the system.
- Check the heat pump breakers/isolators in the consumer unit are on.
What the engineer will check
- Diagnose via KSM service menu / Cloud.Kronoterm technician access.
- Measure supply voltage and phase sequence/presence at the unit.
Who to ask for: heat pump engineer (Kronoterm-trained).
Certification: Electrical competence.
What you might notice
Sources
- KRONOTERM KT-2A Controller operating instructions (technician, user) - ADAPT, VERSI, ETERA, WPLV and ADAPT MAX systems, 17-19-45-6702-08 ↗ · 17-19-45-6702-08 · page 38 · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026