Carel AL001

What does Carel AL001 mean?

AL001 on the Carel Heos system chiller controller (0300081EN) indicates an error in the number of retain memory writings. The controller has exceeded the allowed frequency of writes to its retain (non-volatile) memory storage area, which triggers this alarm to protect memory longevity. Manual reset is required and the alarm does not cause any system shutdown on its own.

Symptoms

• AL001 displayed on the Heos system controller.
• No direct impact on chiller or pump operation at the AL001 level alone.
• Manual reset is required to clear the alarm.
• Repeated AL001 events indicate accelerating memory write frequency.

Common causes

• Application variables that are written to retain memory are changing at an excessively high rate.
• Controller firmware fault causing abnormal retain memory write frequency.
• Unstable input signals (e.g., fluctuating analog sensor) triggering repeated parameter saves.
• External supervisory system sending excessive write commands to retain variables.
• Hardware deterioration of the retain memory chip nearing end of write cycle life.

Diagnostic steps

1. 01

   Record and manually reset AL001

   Note the date and time of AL001 in the service log. Manually reset the alarm from the Heos system controller alarm menu.

2. 02

   Check for accompanying alarms that may indicate root cause

   Review the full alarm log. If AL001 appears alongside frequent sensor alarms or communication errors, unstable inputs may be driving excessive memory writes.

3. 03

   Inspect sensor inputs for unstable or noisy signals

   Check all analog sensor inputs connected to the pCO controller for noise or oscillation. Shield sensor cables separately from power wiring.

4. 04

   Review supervisory system write commands

   If a BMS or supervisory system is connected, verify it is not issuing excessive setpoint writes to the controller at a rate that stresses retain memory.

5. 05

   Monitor recurrence frequency

   If AL001 recurs frequently (more than a few times per day), escalate to a Carel-authorized technician for deeper diagnostics of the retain memory health.

When to call a professional

If AL001 recurs frequently or is accompanied by AL002 (retain memory write error), the controller's non-volatile memory may be approaching failure. Controller board replacement requires a Carel-certified technician who can restore system configuration and re-commission the chiller.