799 on an alpha innotec heat pump: ModBus connection lost ASB: No ModBus communication with the ASB board for at least 10 s. Reset autom
Short answer
On an alpha innotec heat pump, 799 means: ModBus connection lost ASB: No ModBus communication with the ASB board for at least 10 s. Reset autom. 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: ModBus connection lost ASB: No ModBus communication with the ASB board for at least 10 s. Reset autom.
When it shows: No ModBus communication with the ASB board for at least 10 s. Reset autom.
Likely causes:
- ASB board Modbus wiring.
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.
Resetting itself: yes.
Manual reset: automatic.
What you can check
- Note the error number and text shown on the Luxtronik display.
- The controller resets this automatically after the stated time - wait for the automatic restart before calling.
- Acknowledge the message by pressing the rotary pushbutton for about 7 seconds (as the Luxtronik manual permits); if the same error reappears, contact your installer or ait customer service with the error number.
- Check the heat pump breakers/isolator at the consumer unit are on (do not open any casing).
What the engineer will check
- Check ModBus - ASB board wiring.
Who to ask for: heat pump service engineer (electrical/controls).
What you might notice
Sources
- Operating manual Luxtronik heating and heat pump control Part 2 (UK) 83055400lUK - 2.1 ↗ · 83055400lUK 2.1 · page 55 · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026