E3 on a Worcester Bosch Bosch Compress 2000 AWF: Alarm table: Leaving water temperature sensor T1 failure / Troubleshooting table: Error of the backup heater's heat exchanger outlet T1 temperature sensor
Short answer
On a Worcester Bosch heat pump, E3 means: Alarm table: Leaving water temperature sensor T1 failure / Troubleshooting table: Error of the backup heater's heat exchanger outlet T1 temperature sensor. 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: Leaving water temperature sensor T1 failure / Troubleshooting table: Error of the backup heater's heat exchanger outlet T1 temperature sensor.
Part involved: T1 total leaving water temperature sensor.
When it shows: Leaving water temperature sensor T1 failure.
Likely causes:
- Sensor connector loose, wet/water ingress in connector, or sensor faulty (manual: reconnect, dry and seal connector with waterproof adhesive, or replace sensor).
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 sensor connector seating and moisture; measure sensor resistance; replace sensor if faulty (inside unit casing - isolate power, wait 10 min for DC bus discharge).
Who to ask for: heat pump installer / electrician.
Certification: Electrical work to BS 7671 by competent person.
What you might notice
Sources
- Installation and operating instructions Compress 2000 AWF CS2000AWF 4-30 R-S/T ↗ · 6721859133 (2025/10) · page 128; 135 · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026