Additional-heat-is-now-working-at-its-highest-temperature on a Worcester Bosch Greenstore LECP ground source heat pump: Additional heat is now working at its highest temperature
Short answer
On a Worcester Bosch heat pump, Additional-heat-is-now-working-at-its-highest-temperature means: Additional heat is now working at its highest temperature. The heat pump keeps running. An engineer is needed to fix the cause.
Reviewed 23 September 2026 · 1 source
What it means
The manual says: Additional heat is now working at its highest temperature.
Part involved: electric additional heat / T8.
When it shows: T8 approaches highest permitted temperature in additional heat mode; heater stepped down.
Likely causes:
- T8 approaches highest permitted temperature in additional heat mode; heater stepped down.
Is it safe?
| Does the heat pump stop? | No |
|---|---|
| Severity | Warning |
| Engineer needed? | Yes |
The heat pump keeps running.
Resetting itself: yes.
Manual reset: Automatic.
What you can check
- Read and note the full alarm text and category letter shown on the controller and pass it to your installer.
What the engineer will check
- Diagnose per chapter 21: T8 approaches highest permitted temperature in additional heat mode; heater stepped down.
Who to ask for: heat pump installer / heating engineer.
Certification: None specific for hydraulic checks; MCS-certified installer recommended for system changes.
What you might notice
Sources
- Installation, Commissioning and Servicing Instructions Worcester Greenstore LECP GSHP (System/Combi 6-11 kW) ↗ · 6 720 806 768 (2013/02) · page 62 · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026