EC on a Worcester Bosch heat pump: Alarm table: DHW additional storage tank sensor Tbt2 failure
Short answer
On a Worcester Bosch heat pump, EC means: Alarm table: DHW additional storage tank sensor Tbt2 failure. The heat pump keeps running with some functions stopped. An engineer is needed to fix the cause. The wording differs by model range — each is shown below.
Reviewed 23 September 2026 · 2 sources
What it means
On the Bosch Compress 2000 AWF (R32 all-in-one monobloc)
The manual says: Alarm table: DHW additional storage tank sensor Tbt2 failure.
Part involved: Tbt2 additional storage tank sensor.
When it shows: DHW additional storage tank sensor Tbt2 failure.
Likely causes:
- Sensor failure (troubleshooting table has no EC entry).
On the Greenstar Plus Hybrid (air to water heat pump + Worcester boiler)
The manual says: Time limit exceeded for start of operation.
Part involved: internal-external unit communication.
When it shows: Time limit exceeded for start of operation.
Likely causes:
- System not initialised 4 min after start: contacts/wiring, cable sizing/polarity, noise.
Is it safe?
On the Bosch Compress 2000 AWF (R32 all-in-one monobloc)
| 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.
On the Greenstar Plus Hybrid (air to water heat pump + Worcester boiler)
| 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: unknown.
Manual reset: Codes read via outdoor unit LEDs or service tool 7-716-161-051; SW1-2 DIP switch cancels fault displays (engineer).
What you can check
On the Bosch Compress 2000 AWF (R32 all-in-one monobloc)
- 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.
On the Greenstar Plus Hybrid (air to water heat pump + Worcester boiler)
- Read and note the full FW200/hybrid manager fault code shown on the controller and pass it to your installer.
- Check the heat pump isolator and consumer-unit breaker(s) are switched on; if a breaker has tripped more than once, leave it off and call an engineer.
- Check the outdoor unit is not blocked by leaves, snow, ice or other debris (do not open the casing).
What the engineer will check
On the Bosch Compress 2000 AWF (R32 all-in-one monobloc)
- 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.
On the Greenstar Plus Hybrid (air to water heat pump + Worcester boiler)
- System not initialised 4 min after start: contacts/wiring, cable sizing/polarity, noise.
Who to ask for: heat pump installer / electrician.
Certification: Electrical work to BS 7671 by competent person.
What you might notice
What owners and engineers report
1 owner and engineer report mentions this.
- Keeps stopping / cutting out on the Bosch Compress 2000 AWF (R32 all-in-one monobloc): 1 report
Sources
- Installation and operating instructions Compress 2000 AWF CS2000AWF 4-30 R-S/T ↗ · 6721859133 (2025/10) · page 128 · Reviewed 23 September 2026
- Installation and Maintenance Instructions Greenstar Plus Hybrid ↗ · 6 720 803 687 (2012/11) · page 63 · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026