PP on a Worcester Bosch Bosch Compress 2000 AWF: Alarm table: Abnormal temperature difference between entering and leaving water / Troubleshooting table: The inlet water temperature is higher than the outlet water temperature in heating mode
Short answer
On a Worcester Bosch heat pump, PP means: Alarm table: Abnormal temperature difference between entering and leaving water / Troubleshooting table: The inlet water temperature is higher than the outlet water temperature in heating mode. 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: Abnormal temperature difference between entering and leaving water / Troubleshooting table: The inlet water temperature is higher than the outlet water temperature in heating mode.
Part involved: Tw_in / Tw_out sensors, 4-way valve.
When it shows: Abnormal temperature difference between entering and leaving water.
Likely causes:
- Inlet/outlet water sensor connector loose; TW_in or TW_out sensor faulty; 4-way valve blocked (restart to change direction); 4-way valve faulty.
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.
- 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
- Check sensors; restart to free 4-way valve; replace valve if faulty.
Who to ask for: F-gas refrigeration engineer / heat pump installer.
Certification: F-gas certification (Category I) required for refrigerant circuit work; qualified electrician for electrical work.
What you might notice
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