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Heat pumps · Error codes · iDM Energiesysteme
091iDM Energiesysteme · TERRA SW (2013)

091 on an iDM Energiesysteme TERRA SW: Central unit 2 not online: Communication problem - slave board A7 not found

Short answer

On an iDM Energiesysteme heat pump, 091 means: Central unit 2 not online: Communication problem - slave board A7 not found. 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: Central unit 2 not online: Communication problem - slave board A7 not found.

Part involved: Central unit 2 not online.

When it shows: Communication problem - slave board A7 not found.

Is it safe?

Does the heat pump stop?Not stated
Engineer needed?Yes

The manual does not say whether the heat pump stops.

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

A code explains what the controller detected, not a confirmed root cause.

Reviewed: 23 September 2026