C0 on a Worcester Bosch Bosch Compress 2000 AWF: Alarm table: Multiple units configured as Master in the M/S network. / Troubleshooting table: multiple units configured as master in the master - slave network (printed 'CO')
Short answer
On a Worcester Bosch heat pump, C0 means: Alarm table: Multiple units configured as Master in the M/S network. / Troubleshooting table: multiple units configured as master in the master - slave network (printed 'CO'). 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: Multiple units configured as Master in the M/S network. / Troubleshooting table: multiple units configured as master in the master - slave network (printed 'CO').
Part involved: cascade master/slave configuration.
When it shows: Multiple units configured as Master in the M/S network.
Likely causes:
- More than one unit configured as master.
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
- Configure only one unit as master.
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 · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026