5199 on a Worcester Bosch Bosch Compress 5800i Hybrid Heat Pump: Dry running of the hybrid circulation pump (PH0)
Short answer
On a Worcester Bosch heat pump, 5199 means: Dry running of the hybrid circulation pump (PH0). The heat pump keeps running with some functions stopped. An engineer is needed to fix the cause.
Reviewed 23 September 2026 · 1 source
What it means
The manual says: Dry running of the hybrid circulation pump (PH0).
Part involved: hybrid circulation pump PH0.
When it shows: Dry running of the hybrid circulation pump (PH0).
Likely causes:
- No water in system; air in system.
Is it safe?
| Does the heat pump stop? | Partly |
|---|---|
| Severity | Fault — clears by itself when the condition goes |
| Engineer needed? | Yes |
The heat pump keeps running with some functions stopped.
Resetting itself: Clears when cause removed.
Manual reset: Manual 12.1: fault indications can be reset on the control unit in the diagnostic menu with Reset.
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.
- If the hybrid system stops using the heat pump, the gas boiler may still provide heat - do not attempt repairs yourself.
What the engineer will check
- Fill system; start bleeding function.
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/operating instructions Hybrid-Set CSH5800iAW O ↗ · 6721875003 (2024/08) · page 40 · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026