A31-3021 on a Worcester Bosch heat pump: Heating circuit 1…4 flow temperature sensor faulty – standby mode active (A31/3021 = heating circuit 1…A34/3024 = heating circuit 4)
Short answer
On a Worcester Bosch heat pump, A31-3021 means: Heating circuit 1…4 flow temperature sensor faulty – standby mode active (A31/3021 = heating circuit 1…A34/3024 = heating 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: Heating circuit 1…4 flow temperature sensor faulty – standby mode active (A31/3021 = heating circuit 1…A34/3024 = heating circuit 4).
Part involved: heating circuit flow temperature sensor.
When it shows: Heating circuit 1…4 flow temperature sensor faulty – standby mode active (A31/3021 = heating circuit 1…A34/3024 = heating circuit 4).
Likely causes:
- Configuration requires flow sensor; lead between heating circuit module and sensor faulty; faulty sensor; faulty heating circuit module.
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: Clears when cause is removed.
Manual reset: User guides (7001i/7400i AWE, 3400i AWS, section 3.5): user may confirm the fault by pressing the selector; if it persists call the contractor with fault code, sub-code and user-interface 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.
- Confirm/acknowledge the fault once at the controller (press selector) as the user guide allows; if it returns, call the installer.
What the engineer will check
- Check config, lead, sensor resistance, terminal voltage; replace sensor or module.
Who to ask for: heat pump installer / controls engineer.
Certification: None specific; electrical isolation required before wiring checks.
What you might notice
Sources
- Installation instructions User interface HPC 410 ↗ · 6721832682 (2021/02) · page 18 · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026