Heat pumps · Error codes · iDM Energiesysteme
516iDM Energiesysteme · TERRA SW (2013)
516 on an iDM Energiesysteme TERRA SW: Outdoor unit communication: Communication fault on the Modbus link between indoor unit and outdoor unit
Short answer
On an iDM Energiesysteme heat pump, 516 means: Outdoor unit communication: Communication fault on the Modbus link between indoor unit and outdoor unit. 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: Outdoor unit communication: Communication fault on the Modbus link between indoor unit and outdoor unit.
Part involved: Outdoor unit communication.
When it shows: Communication fault on the Modbus link between indoor unit and outdoor unit.
Is it safe?
| Does the heat pump stop? | Yes |
|---|---|
| Engineer needed? | Yes |
The heat pump stops until the fault clears or is reset.
What you can check
- Note the fault number and text shown after tapping the fault symbol on the Navigator display. If the fault recurs several times, contact iDM customer service/your installer.
What the engineer will check
- Diagnose per iDM service documentation for the unit (not obtained): check the monitored circuit/component named in the fault.
Who to ask for: heat pump engineer.
What you might notice
Sources
- IDM Wärmepumpen mit Navigatorregelung 2.0 - Bedienungsanleitung (812152 Rev.3) ↗ · 812152 Rev.3 · page p.73 · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026