E2 on a Worcester Bosch heat pump: Alarm table: Communication error between user interface and hydraulic module / Troubleshooting table: Communication error between the user interface and the main hydraulic module control board
Short answer
On a Worcester Bosch heat pump, E2 means: Alarm table: Communication error between user interface and hydraulic module / Troubleshooting table: Communication error between the user interface and the main hydraulic module control board. 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 · 2 sources
What it means
On the Bosch Compress 2000 AWF (R32 all-in-one monobloc)
The manual says: Alarm table: Communication error between user interface and hydraulic module / Troubleshooting table: Communication error between the user interface and the main hydraulic module control board.
Part involved: user interface (HMI) to hydraulic module bus.
When it shows: Communication error between user interface and hydraulic module.
Likely causes:
- No connection between wired control and unit; communication wires in wrong sequence; strong magnetic field/electrical interference (lifts, transformers); interference from power cables along control cable route.
On the Greenstar Plus Hybrid (air to water heat pump + Worcester boiler)
The manual says: Flow temperature sensor faulty (status L) - temperature sensor short/open circuit, condenser outlet.
Part involved: hybrid control module / FW200.
When it shows: Flow temperature sensor faulty (status L) - temperature sensor short/open circuit, condenser outlet.
Likely causes:
- Condenser outlet sensor short or open circuit; check contacts, wiring, sensor.
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).
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.
- 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.
What the engineer will check
On the Bosch Compress 2000 AWF (R32 all-in-one monobloc)
- Check HMI cable continuity, wiring order, segregation from mains cables; add shielding/relocate.
Who to ask for: heat pump installer / controls engineer.
Certification: None specific; electrical isolation required before wiring checks.
On the Greenstar Plus Hybrid (air to water heat pump + Worcester boiler)
- Condenser outlet sensor short or open circuit; check contacts, wiring, sensor.
Who to ask for: heat pump installer / electrician.
Certification: Electrical work to BS 7671 by competent person.
What you might notice
Sources
- Installation and operating instructions Compress 2000 AWF CS2000AWF 4-30 R-S/T ↗ · 6721859133 (2025/10) · page 128; 135 · Reviewed 23 September 2026
- Installation and Maintenance Instructions Greenstar Plus Hybrid ↗ · 6 720 803 687 (2012/11) · page 58 · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026