Alarm-heat-pump on a Worcester Bosch Greensource Split HP Hydrolight / Hydrocomfort: Alarm: Alarm heat pump
Short answer
On a Worcester Bosch heat pump, Alarm-heat-pump means: Alarm: Alarm heat pump. 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: Alarm heat pump.
Part involved: outdoor unit (ODU).
When it shows: Outdoor unit has developed a fault; signal cable S2/S3; mains voltage; brief supply interruption.
Likely causes:
- Outdoor unit has developed a fault; signal cable S2/S3; mains voltage; brief supply interruption.
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.
- Check the outdoor unit is not blocked by leaves, snow, ice or other debris (do not open the casing).
- Acknowledge the alarm once on the control panel; if it returns, call the installer.
What the engineer will check
- Check S2/S3 signal cables, read fault code with diagnostic tool (accessory), check mains voltage, power down both units together then restart after 1 min.
Who to ask for: F-gas refrigeration engineer / heat pump installer.
Certification: F-gas certification (Category I) required for refrigerant circuit work; qualified electrician for electrical work.
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