err-phase-seq on a Thermia Diplomat: Alarm that indicates that there is an incorrect phase sequence to the compressor. Only display and only the first 10 minutes
Short answer
On a Thermia heat pump, err-phase-seq means: Alarm that indicates that there is an incorrect phase sequence to the compressor. Only display and only the first 10 minutes. The manual does not say whether the heat pump stops. An engineer is needed to fix the cause.
Reviewed 23 September 2026 · 1 source
What it means
The manual says: Alarm that indicates that there is an incorrect phase sequence to the compressor. Only display and only the first 10 minutes.
Part involved: phase sequence.
Is it safe?
| Does the heat pump stop? | Not stated |
|---|---|
| Severity | Warning |
| Engineer needed? | Yes |
The manual does not say whether the heat pump stops.
What you can check
- Note the exact alarm text. User guide VUGFD302: can be displayed with mains interference, e.g. after a temporary power cut - reset (operating mode OFF then back) and if necessary switch the power supply off for a minute or two at the isolator. Acknowledge once by setting operating mode OFF then back; 'Other alarm message: reset the alarm; if the alarm remains, contact a service technician' (VUGFD302 p.16).
What the engineer will check
- Swap two incoming phases if sequence genuinely wrong. Causes per the equivalent Danfoss service instructions VMGFC302 (same Danfoss-era controller) - not stated in the Thermia user manual.
Who to ask for: heat pump engineer.
Certification: Qualified electrician / heat pump engineer (electrical fault-finding).
What you might notice
Sources
- User manual Atria, Atria Duo, Atria Duo Optimum, Atria Optimum, Comfort, Diplomat, Diplomat Duo, Diplomat Duo Optimum (G2), Diplomat Optimum (G2) - 086U6297 Rev. 6 EN ↗ · 086U6297 Rev. 6 · page printed p.42 (PDF p.44) · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026