Heat pumps · Error codes · Danfoss
21Danfoss · DHP-AT
21 on a Danfoss DHP-AT: Heating coil sensor (T7) failure
Short answer
On a Danfoss heat pump, 21 means: Heating coil sensor (T7) failure. 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: Heating coil sensor (T7) failure.
Part involved: Heating coil sensor (T7) failure.
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.
What you can check
- Note the 2-digit code. If the code persists, call an engineer.
What the engineer will check
- Measure sensor/cable resistance or check the indicated circuit; consult VMGFI302 section 4.4 check and safety functions.
Who to ask for: heat pump engineer.
What you might notice
Sources
- Installation Guide DHP-AT - Installation and service manual (VMGFI302 / AN089486453198) ↗ · VMGFI302 · page p.32 (section 10.1.1); safety functions pp.16-17 · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026