EVCO AL02

What does EVCO AL02 mean?

AL02 (displayed as oFFt) on the Evco EV3 HRV and EVD HRV heat recovery ventilation controllers indicates that the unit has been switched off by its time-band (weekly scheduler) programme. This is an informational status code rather than a fault alarm — it tells the operator that the controller deliberately powered down all loads because the current time falls within a scheduled off period. The controller resets automatically when the scheduled on period begins.

Symptoms

• oFFt or AL02 displayed on the HRV controller screen.
• All HRV loads — supply fan, extract fan, heat recovery wheel, heating/cooling outputs — are switched off.
• No manual fault or probe error is present; the unit is responding to its programmed schedule.
• Alarm self-clears automatically when the next scheduled on period begins.
• Loads restart with preset timing sequences (soft start) when the time band switches back to on.

Common causes

• Time-band programme parameter (t01 set to 2 or 3) has scheduled the current time block as an off period.
• Controller clock has drifted or was incorrectly set, causing the off period to be active at the wrong time of day.
• Weekly programme was recently modified and an unintended off block was created.
• Daylight saving time transition shifted the clock without a corresponding programme adjustment.
• Controller clock battery has discharged, resetting the clock and potentially misaligning the schedule.

Diagnostic steps

1. 01

   Confirm the controller is in scheduled off mode

   Verify that oFFt is displayed and no probe or fault alarm is co-active. oFFt alone confirms a time-band shutdown rather than an equipment failure — no corrective action is needed if the schedule is intentional.

2. 02

   Check the current time and date on the controller

   Navigate to the clock settings menu and confirm the displayed time and date are correct. An incorrect clock causes the scheduler to activate off periods at the wrong times. Correct the time if it has drifted.

3. 03

   Review the time-band programme settings

   Access the scheduler or time-band menu and check which time blocks are configured as off periods. Confirm the off period covering the current time is intentional. Adjust the programme if an incorrect block is configured as off.

4. 04

   Override the time band if immediate operation is needed

   Most EVCO HRV controllers allow a temporary manual override that bypasses the time-band programme and restarts the unit. Consult the controller operating manual for the override key sequence. The override typically lasts until the next scheduled transition.

5. 05

   Confirm automatic restart at the next on period

   If the off period is correct and intentional, oFFt will clear automatically when the scheduled on period begins. Monitor the controller at the expected start time to confirm the unit restarts correctly.

When to call a professional

oFFt does not indicate a hardware fault and typically does not require a technician. However, if the time-band programme was modified by an unauthorised person or the unit is failing to restart at the expected time despite a correct clock setting, engage a licensed HVAC controls technician to review the full programmer configuration. In critical ventilation applications such as server rooms, laboratories, or healthcare environments, unscheduled off periods may have compliance or safety implications that require facilities management review.