Heat pumps · Error codes · Danfoss
com-error-expansion-cardDanfoss · DHP-AQ
com-error-expansion-card on a Danfoss DHP-AQ: Communication broken between display card and expansion card (indoor)
Short answer
On a Danfoss heat pump, com-error-expansion-card means: Communication broken between display card and expansion card (indoor). 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: Communication broken between display card and expansion card (indoor).
Part involved: expansion card.
Likely causes:
- Communication cable/connection or card fault.
Is it safe?
| Does the heat pump stop? | Partly |
|---|---|
| Engineer needed? | Yes |
The heat pump keeps running with some functions stopped.
Manual reset: Set operating mode OFF then back to the desired mode.
What you can check
- Note the exact alarm text. The manual allows acknowledging by setting operating mode OFF then back once; if the alarm returns, call an engineer.
What the engineer will check
- Check/replace communication cable; test expansion card.
Who to ask for: heat pump engineer.
Certification: Qualified electrician / heat pump engineer (electrical fault-finding).
What you might notice
Sources
- Service Instructions DHP-AQ (VMGFJ202) ↗ · VMGFJ202 · page p.11 · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026