Heat pumps · Error codes · Atlantic
ODU3-21FAtlantic · Alféa Hybrid Duo (heat pump + integrated fuel-oil boiler)
ODU3-21F on an Atlantic Alféa Hybrid Duo: Connection error with the hydraulic module
Short answer
On an Atlantic heat pump, ODU3-21F means: Connection error with the hydraulic module. 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: Connection error with the hydraulic module.
Likely causes:
- Communication/connection fault between hydraulic unit and outdoor unit (or between boards), or incompatible combination.
Is it safe?
| Does the heat pump stop? | Yes |
|---|---|
| Severity | Fault — clears by itself when the condition goes |
| Engineer needed? | Yes |
The heat pump stops until the fault clears or is reset.
What you can check
- Check the heat pump isolator and consumer-unit breakers are on (do not open any casing).
- Note the error number/LED pattern shown and give it to your installer.
What the engineer will check
- Check interconnection cable and terminals between indoor and outdoor units.
- Check board connectors and unit combination.
Who to ask for: heat pump / electrical.
Sources
- alféa hybrid duo Installation and commissioning instructions (doc 1440-13) ↗ · 1440-13 · page 67 · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026