Low-mains-voltage on a Worcester Bosch Greensource Split HP Hydrolight / Hydrocomfort: Alarm: Low mains voltage
Short answer
On a Worcester Bosch heat pump, Low-mains-voltage means: Alarm: Low mains voltage. 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: Low mains voltage.
Part involved: mains voltage.
When it shows: Mains voltage below 170 V for more than one hour (info symbol first).
Likely causes:
- Mains voltage below 170 V for more than one hour (info symbol first).
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.
- 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.
- Acknowledge the alarm once on the control panel; if it returns, call the installer.
What the engineer will check
- Check mains voltage.
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