E8 on a Worcester Bosch Bosch Compress 2000 AWF: Alarm table: Water flow failure (displayed three times and can be reset after minutes) / Troubleshooting table: Water flow-rate error
Short answer
On a Worcester Bosch heat pump, E8 means: Alarm table: Water flow failure (displayed three times and can be reset after minutes) / Troubleshooting table: Water flow-rate error. 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 table: Water flow failure (displayed three times and can be reset after minutes) / Troubleshooting table: Water flow-rate error.
Part involved: water flow / circulation.
When it shows: Water flow failure (displayed three times and can be reset after minutes).
Likely causes:
- Shut-off valves not fully open; dirty water filter; air in system; water pressure below 1 bar; pump speed not at maximum; expansion tank failure; circuit resistance too high for pump; during defrost - backup heater supply/fuses; pump fuse or PCB fuse blown.
Is it safe?
| Does the heat pump stop? | Yes |
|---|---|
| Severity | Fault — clears by itself when the condition goes |
| Engineer needed? | Yes |
The heat pump stops until the fault clears or is reset.
Resetting itself: yes.
Manual reset: Manual 13.2: switch the unit off and on again to reset the safety device; if reset fails contact dealer. Manual 11.4 warns repeated resets can cause irreversible damage.
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.
- Manual 13.2: one off/on restart may be tried; if the code returns, stop and call an engineer - repeated resets can damage the unit.
What the engineer will check
- Open valves, clean filter, vent system, repressurise to >1 bar, set pump speed, check expansion vessel, check backup heater supply and fuses, check pump and PCB fuses.
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
What owners and engineers report
1 owner and engineer report mentions this.
- Keeps stopping / cutting out on the Bosch Compress 2000 AWF (R32 all-in-one monobloc): 1 report
Sources
- Installation and operating instructions Compress 2000 AWF CS2000AWF 4-30 R-S/T ↗ · 6721859133 (2025/10) · page 128; 136 · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026