Heat pumps · Error codes · Cool Energy
AL139Cool Energy · inverTech (R410A, Carel control)
AL139 on a Cool Energy inverTech: Low temp. alarm
Short answer
On a Cool Energy heat pump, AL139 means: Low temp. alarm. 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: Low temp. alarm.
Is it safe?
| Does the heat pump stop? | Yes |
|---|---|
| Engineer needed? | Yes |
The heat pump stops until the fault clears or is reset.
What you can check
- Read and note the code shown on the controller display, then contact your installer or service engineer.
- Check the heating system pressure gauge reading against the value in your handover documents (manufacturer commissioning values: typically 1-2 bar) and that the filling loop is closed.
- Check the outdoor unit/air grilles are not blocked by debris, leaves or snow.
What the engineer will check
- Check water flow rate and temperature sensors.
- Check set-points and system design temperatures.
- Check refrigerant charge.
Who to ask for: heat pump engineer.
Certification: None specific.
What you might notice
Sources
- Cool Energy inverTech Monoblock Series Heat Pump Water Heaters - Installation and Users Guide v6.6 (2020) ↗ · Version 6.6 · page 32 · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026