HP on a Worcester Bosch heat pump: Alarm table: Cooling mode low pressure protection (in 1 hour, low pressure is below 0.6 MPa three consecutive times, can be reset automatically) / Troubleshooting table: Low pressure protection (Pe < 0.6) tripped 3 times in one hour
Short answer
On a Worcester Bosch heat pump, HP means: Alarm table: Cooling mode low pressure protection (in 1 hour, low pressure is below 0.6 MPa three consecutive times, can be reset automatically) / Troubleshooting table: Low pressure protection (Pe < 0.6) tripped 3 times in one hour. The heat pump stops until the fault clears or is reset. An engineer is needed to fix the cause. The wording differs by model range — each is shown below.
Reviewed 23 September 2026 · 3 sources
What it means
On the Bosch Compress 2000 AWF (R32 all-in-one monobloc)
The manual says: Alarm table: Cooling mode low pressure protection (in 1 hour, low pressure is below 0.6 MPa three consecutive times, can be reset automatically) / Troubleshooting table: Low pressure protection (Pe < 0.6) tripped 3 times in one hour.
Part involved: low pressure protection (cooling).
When it shows: Cooling mode low pressure protection (in 1 hour, low pressure is below 0.6 MPa three consecutive times, can be reset automatically).
Likely causes:
- See P0.
On the Greenstar Plus Hybrid (air to water heat pump + Worcester boiler)
The manual says: External unit / water flow rate fault; heat pump flow switch fault during self-test (status L).
Part involved: hybrid control module / FW200.
When it shows: External unit / water flow rate fault; heat pump flow switch fault during self-test (status L).
Likely causes:
- Fault affecting heat pump / water flow interrupted: check LED signals, throughput, filter, flow switch, system.
On the Greenstore ground source heat pump (original, System & Combi)
The manual says: High pressure switch (HP).
Part involved: high pressure switch.
When it shows: High pressure switch (HP).
Likely causes:
- Insufficient primary flow (pump stopped, valves closed); primary filter blocked; air in primary circuit.
Is it safe?
On the Bosch Compress 2000 AWF (R32 all-in-one monobloc)
| 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.
On the Greenstar Plus Hybrid (air to water heat pump + Worcester boiler)
| Does the heat pump stop? | Yes |
|---|---|
| Severity | Fault — needs a manual reset once the cause is fixed |
| Engineer needed? | Yes |
The heat pump stops until the fault clears or is reset.
Resetting itself: no.
Manual reset: Hold Back button on hybrid control module 5 s to restart after fault is rectified (installer).
On the Greenstore ground source heat pump (original, System & Combi)
| Does the heat pump stop? | Yes |
|---|---|
| Severity | Fault — needs a manual reset once the cause is fixed |
| Engineer needed? | Yes |
The heat pump stops until the fault clears or is reset.
Resetting itself: no.
Manual reset: Press Ackn. on the control panel; heat pump restarts within 15 minutes if there is demand. Some causes need a reset button/MCB on the heat pump (engineer).
What you can check
On the Bosch Compress 2000 AWF (R32 all-in-one monobloc)
- Read and note the full code (and sub-code) shown on the controller and pass it to your installer.
- Check the outdoor unit is not blocked by leaves, snow, ice or other debris (do not open the casing).
- 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.
On the Greenstar Plus Hybrid (air to water heat pump + Worcester boiler)
- Read and note the full code (and sub-code) shown on the controller and pass it to your installer.
- Check whether the boiler display also shows a fault (manual: if the boiler shows a fault the heat pump is not faulty) and report both to the engineer.
- Check the heating system pressure gauge reading (Bosch guidance is typically 1-2 bar when cold); report low pressure to your installer.
On the Greenstore ground source heat pump (original, System & Combi)
- Read and note the full alarm text and code in brackets 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.
- Press the Ackn. button once as the manual describes (manual: no risk in resetting an alarm); contact technical support if the alarm repeats.
What the engineer will check
On the Bosch Compress 2000 AWF (R32 all-in-one monobloc)
- Follow P0 checks.
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.
On the Greenstar Plus Hybrid (air to water heat pump + Worcester boiler)
- Fault affecting heat pump / water flow interrupted: check LED signals, throughput, filter, flow switch, system.
Who to ask for: heat pump installer / heating engineer.
Certification: None specific for hydraulic checks; MCS-certified installer recommended for system changes.
On the Greenstore ground source heat pump (original, System & Combi)
- Check pump, valves, filter; vent; increase pump speed.
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
4 owner and engineer reports mention this.
- Keeps stopping / cutting out on the Bosch Compress 2000 AWF (R32 all-in-one monobloc): 1 report
- No heating on the Greenstore ground source heat pump (original, System & Combi): 2 reports
- Keeps stopping / cutting out on the Greenstore ground source heat pump (original, System & Combi): 1 report
Sources
- Installation and operating instructions Compress 2000 AWF CS2000AWF 4-30 R-S/T ↗ · 6721859133 (2025/10) · page 129; 137 · Reviewed 23 September 2026
- Installation and Maintenance Instructions Greenstar Plus Hybrid ↗ · 6 720 803 687 (2012/11) · page 58 · Reviewed 23 September 2026
- Worcester Greenstore 6/7/9/11 kW System Installation, Commissioning & Servicing ↗ · 8-716-112-860 Issue c · page 36 · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026