Heat pumps · Error codes · Worcester Bosch
5594Worcester Bosch · Bosch Compress 5800i AW (R290 monobloc)
5594 on a Worcester Bosch Bosch Compress 5800i AW: Alarm: Z1 air in system
Short answer
On a Worcester Bosch heat pump, 5594 means: Alarm: Z1 air in system. 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: Z1 air in system.
Part involved: primary circuit.
When it shows: Alarm: Z1 air in system.
Likely causes:
- Air in appliance; flow obstructed by valve; faulty primary circulation pump.
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.
- Check the heating system pressure gauge reading (Bosch guidance is typically 1-2 bar when cold); report low pressure to your installer.
What the engineer will check
- Vent per installation instructions; open valves; check/vent/replace primary 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 21 · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026