Heat pumps · Error codes · Thermia
high-returnThermia · Diplomat
high-return on a Thermia Diplomat: Alarm that indicates that high return temperature prevents the compressor's operation
Short answer
On a Thermia heat pump, high-return means: Alarm that indicates that high return temperature prevents the compressor's operation. The heat pump keeps running with some functions stopped. An engineer is needed to fix the cause.
Reviewed 23 September 2026 · 1 source
What it means
The manual says: Alarm that indicates that high return temperature prevents the compressor's operation.
Part involved: return temperature.
Is it safe?
| Does the heat pump stop? | Partly |
|---|---|
| Severity | Fault — clears by itself when the condition goes |
| Engineer needed? | Yes |
The heat pump keeps running with some functions stopped.
Resetting itself: Yes, when condition clears (inferred).
What you can check
- Note the exact alarm text. Check the heating-system pressure gauge is in the range given in the user guide (Thermia/Danfoss: 1-1.5 bar when cold) - do not top up yourself unless you have been shown how; check radiator/underfloor valves and room thermostats are open. 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
- Check curve/MAX, hot water stop temperature, emitter flow. 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.
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