5485 on a Worcester Bosch heat pump: Circulation to heat pump too low (Zu geringer Umlauf zur Wärmepumpe)
Short answer
On a Worcester Bosch heat pump, 5485 means: Circulation to heat pump too low (Zu geringer Umlauf zur Wärmepumpe). The heat pump keeps running with some functions stopped. An engineer is needed to fix the cause. The wording differs by model range — each is shown below.
Reviewed 23 September 2026 · 2 sources
What it means
On the Bosch Compress 5800i AW (R290 monobloc)
The manual says: Circulation to heat pump too low (Zu geringer Umlauf zur Wärmepumpe).
Part involved: primary circuit flow / PC0.
When it shows: Circulation to heat pump too low (Zu geringer Umlauf zur Wärmepumpe).
Likely causes:
- Primary circuit flow too low.
On the Bosch Compress 5800i Hybrid Heat Pump (CSH5800iAW O)
The manual says: Circulation to heat pump too low.
Part involved: heat pump circuit flow.
When it shows: Circulation to heat pump too low.
Likely causes:
- Additional installations/resistance too high (max pipe length exceeded/incorrect sizing); air in pipework to heat pump; defective pump in heat pump circuit.
Is it safe?
On the Bosch Compress 5800i AW (R290 monobloc)
| 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: Reset/acknowledge via UI 800 fault menu after cause removed.
On the Bosch Compress 5800i Hybrid Heat Pump (CSH5800iAW O)
| 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
On the Bosch Compress 5800i AW (R290 monobloc)
- 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.
On the Bosch Compress 5800i Hybrid Heat Pump (CSH5800iAW O)
- 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
On the Bosch Compress 5800i AW (R290 monobloc)
- Check/clean particle filter; check and vent primary circulation pump PC0.
Who to ask for: heat pump installer / heating engineer.
Certification: None specific for hydraulic checks; MCS-certified installer recommended for system changes.
On the Bosch Compress 5800i Hybrid Heat Pump (CSH5800iAW O)
- Clean wire mesh filter in pump assembly; check piping to specification; vent; replace 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
- Installation/operating instructions Hybrid-Set CSH5800iAW O ↗ · 6721875003 (2024/08) · page 41 · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026