Overloaded-transformer on a Worcester Bosch Greensource Split HP Hydrolight / Hydrocomfort: Alarm: Overloaded transformer
Short answer
On a Worcester Bosch heat pump, Overloaded-transformer means: Alarm: Overloaded transformer. 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: Overloaded transformer.
Part involved: control transformer.
When it shows: Secondary side below 9 V with primary OK; all outputs enabled; manual acknowledgement required.
Likely causes:
- Secondary side below 9 V with primary OK; all outputs enabled; manual acknowledgement required.
Is it safe?
| Does the heat pump stop? | Yes |
|---|---|
| Severity | Fault — needs a manual reset once the cause is fixed |
| Engineer needed? | Yes |
The heat pump stops until the fault clears or is reset.
Resetting itself: no.
Manual reset: Acknowledge by pressing the rotary selector (Acknowledge) on the Hydrolight/Hydrocomfort user interface.
What you can check
- Read and note the full alarm text shown on the controller and pass it to your installer.
- Acknowledge the alarm once on the control panel; if it returns, call the installer.
What the engineer will check
- Check secondary voltage; replace main board.
Who to ask for: heat pump installer / electrician.
Certification: Electrical work to BS 7671 by competent person.
What you might notice
Sources
- Installation, Commissioning and Servicing Instructions Greensource Hydrolight and Hydrocomfort (ODU 7.5-12) ↗ · 6 720 806 629 (2013/02) · page 65 · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026