A21-3141 on a Worcester Bosch heat pump: Sensor for relative humidity in the remote control is faulty (A21/3141: heating/cooling circuit 1 ... A24/3144: circuit 4)
Short answer
On a Worcester Bosch heat pump, A21-3141 means: Sensor for relative humidity in the remote control is faulty (A21/3141: heating/cooling circuit 1 ... A24/3144: circuit 4). 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: Sensor for relative humidity in the remote control is faulty (A21/3141: heating/cooling circuit 1 ... A24/3144: circuit 4).
Part involved: CR 10 H humidity sensor.
When it shows: Sensor for relative humidity in the remote control is faulty (A21/3141: heating/cooling circuit 1 ... A24/3144: circuit 4).
Likely causes:
- Faulty humidity sensor in CR 10 H.
Is it safe?
| Does the heat pump stop? | Partly |
|---|---|
| Severity | Warning |
| Engineer needed? | Yes |
The heat pump keeps running with some functions stopped.
Resetting itself: Clears when cause removed.
Manual reset: CR 10 H manual: if a fault cannot be rectified note fault code and sub-code and contact contractor with ID no.
What you can check
- Read and note the full code (and sub-code) shown on the controller and pass it to your installer.
What the engineer will check
- Replace the faulty CR 10 H.
Who to ask for: heat pump installer / controls engineer.
Certification: None specific; electrical isolation required before wiring checks.
What you might notice
Sources
- CR 10 H room controller manual (multilingual) ↗ · 6720876740 (2017/08) · page 29 · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026