P5 on a Worcester Bosch Bosch Compress 2000 AWF: Alarm table: Twin-Twout, Twout-Twin protection or water supply temperature too high / Troubleshooting table: Protection against high temperature difference between entering and leaving water of the plate heat exchanger
Short answer
On a Worcester Bosch heat pump, P5 means: Alarm table: Twin-Twout, Twout-Twin protection or water supply temperature too high / Troubleshooting table: Protection against high temperature difference between entering and leaving water of the plate heat exchanger. 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: Twin-Twout, Twout-Twin protection or water supply temperature too high / Troubleshooting table: Protection against high temperature difference between entering and leaving water of the plate heat exchanger.
Part involved: plate heat exchanger water temperature difference.
When it shows: Twin-Twout, Twout-Twin protection or water supply temperature too high.
Likely causes:
- Valves not fully open; dirty filter; air in system; water pressure below 1 bar; pump speed not at maximum; expansion tank failure; water circuit resistance too high for pump.
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
- Hydraulic checks as for E8; confirm pump speed setting and system resistance.
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; 138 · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026