Carel AL005

What does Carel AL005 mean?

AL005 on the Carel Heos system controller indicates an LT (low-temperature) pump alarm. The controller has received a fault signal from the LT pump circuit — either from a flow switch, thermal overload, or the pump's alarm contact. The controller responds with an automatic reset and cuts off the LT pump immediately upon alarm activation.

Symptoms

• AL005 displayed on the Heos system controller.
• LT pump shuts off immediately upon alarm.
• LT Chiller loses its water circuit — LT cooling load is interrupted.
• Automatic reset is attempted; pump may restart if the fault clears.

Common causes

• LT pump thermal overload protector has tripped due to overcurrent.
• LT pump motor has failed — winding fault or bearing seizure.
• LT pump flow switch has opened, indicating no flow in the water circuit.
• Air lock or blockage in the LT pump suction line preventing flow.
• Low water level in the LT circuit expansion vessel causing pump cavitation.

Diagnostic steps

1. 01

   Check the LT pump for operation

   Verify the LT pump is running — listen for motor noise and feel for vibration. A pump that is energized but not running indicates a seized motor or blocked impeller.

2. 02

   Inspect the LT pump thermal overload

   Check the thermal overload relay on the LT pump motor starter. If tripped, reset it and measure motor current on all three phases to confirm it is within nameplate ratings.

3. 03

   Check LT circuit water pressure and flow

   Verify water pressure in the LT circuit and confirm flow switch operation. A closed flow switch with no flow indicates air lock, blockage, or pump failure.

4. 04

   Bleed air from the LT circuit

   Open air vent valves on the LT circuit high points to remove any trapped air that could cause pump cavitation and flow loss.

5. 05

   Inspect LT pump strainer

   Check the suction strainer on the LT pump for debris blockage. Clean the strainer basket if restricted.

When to call a professional

If the LT pump motor has failed, shows winding faults, or the pump assembly requires replacement, contact a qualified mechanical technician. Pump replacement on a pressurized hydronic circuit requires proper system isolation, de-pressurization, and recommissioning. Continued operation of the LT circuit without a functioning pump will damage the LT chiller.