H01-5594 on a Worcester Bosch heat pump: Air in the system
Short answer
On a Worcester Bosch heat pump, H01-5594 means: Air in the 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: Air in the system.
Part involved: primary circuit / pump.
When it shows: Air in the system.
Likely causes:
- Heat carrier flow blocked by a valve; faulty primary circulation pump; air in appliance.
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: User guides (7001i/7400i AWE, 3400i AWS, section 3.5): user may confirm the fault by pressing the selector; if it persists call the contractor with fault code, sub-code and user-interface ID no.
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.
- Confirm/acknowledge the fault once at the controller (press selector) as the user guide allows; if it returns, call the installer.
What the engineer will check
- Open valves; check/replace primary pump; carry out purging procedure.
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
- Installation instructions User interface HPC 410 ↗ · 6721832682 (2021/02) · page 19 · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026