H0 on a Worcester Bosch Bosch Compress 2000 AWF: Alarm table: Communication error between indoor unit and unit (continuous communication error for 10 seconds) / Communication error between unit and indoor unit (no communication in 10 seconds) / Troubleshooting table: Communication error between the main PCB B control board and the main hydraulic module control board
Short answer
On a Worcester Bosch heat pump, H0 means: Alarm table: Communication error between indoor unit and unit (continuous communication error for 10 seconds) / Communication error between unit and indoor unit (no communication in 10 seconds) / Troubleshooting table: Communication error between the main PCB B control board 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.
Reviewed 23 September 2026 · 1 source
What it means
The manual says: Alarm table: Communication error between indoor unit and unit (continuous communication error for 10 seconds) / Communication error between unit and indoor unit (no communication in 10 seconds) / Troubleshooting table: Communication error between the main PCB B control board and the main hydraulic module control board.
Part involved: hydraulic module to outdoor main PCB communication.
When it shows: Communication error between indoor unit and unit (continuous communication error for 10 seconds) / Communication error between unit and indoor unit (no communication in 10 seconds).
Likely causes:
- Cable disconnected between main PCB B and hydraulic module board; wires in wrong sequence; strong magnetic field or high-power interference.
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 communication cable and wiring order; shield or relocate.
Who to ask for: heat pump installer / controls engineer.
Certification: None specific; electrical isolation required before wiring checks.
What you might notice
What owners and engineers report
1 owner and engineer report mentions this.
- Heat pump will not start 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