Hd on a Worcester Bosch Bosch Compress 2000 AWF: Alarm table: Communication error between slave and master (this error occurs when several units are connected in parallel) / Troubleshooting table: Communication error between master and slave units
Short answer
On a Worcester Bosch heat pump, Hd means: Alarm table: Communication error between slave and master (this error occurs when several units are connected in parallel) / Troubleshooting table: Communication error between master and slave units. The heat pump keeps running with some functions stopped. 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 slave and master (this error occurs when several units are connected in parallel) / Troubleshooting table: Communication error between master and slave units.
Part involved: cascade master/slave bus.
When it shows: Communication error between slave and master (this error occurs when several units are connected in parallel).
Likely causes:
- Wrong address; incorrect wiring; board fuse; H1-H2 wiring.
Is it safe?
| Does the heat pump stop? | Partly |
|---|---|
| Severity | Fault — clears by itself when the condition goes |
| Engineer needed? | Yes |
The heat pump keeps running with some functions stopped.
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 cascade addresses, wiring and fuse.
Who to ask for: heat pump installer / controls engineer.
Certification: None specific; electrical isolation required before wiring checks.
What you might notice
Sources
- Installation and operating instructions Compress 2000 AWF CS2000AWF 4-30 R-S/T ↗ · 6721859133 (2025/10) · page 129; 137 · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026