5143 on a Worcester Bosch Bosch Compress 5800i AW: Alarm: flow and return swapped between indoor and outdoor unit
Short answer
On a Worcester Bosch heat pump, 5143 means: Alarm: flow and return swapped between indoor and outdoor unit. 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: Alarm: flow and return swapped between indoor and outdoor unit.
Part involved: flow/return connections.
When it shows: Alarm: flow and return swapped between indoor and outdoor unit.
Likely causes:
- Heat pump pipe connection incorrect.
Is it safe?
| Does the heat pump stop? | Yes |
|---|---|
| Severity | Fault — needs a manual reset once the cause is fixed |
| Engineer needed? | Yes |
The heat pump stops until the fault clears or is reset.
Resetting itself: no.
Manual reset: Reset/acknowledge via UI 800 fault menu after cause removed.
What you can check
- Read and note the full code (and sub-code) shown on the controller and pass it to your installer.
What the engineer will check
- Check hydraulic connections at heat pump.
Who to ask for: heat pump installer / heating engineer.
Certification: None specific for hydraulic checks; MCS-certified installer recommended for system changes.
What you might notice
Sources
- Installationsanleitung Bedienfeld UI 800 (Luft-Wasser-Wärmepumpe) 6721833375 ↗ · 6721833375 (2023/09) DE, AT, CH, LU · page 22 · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026