Over-Temperature Fault — Remedies & Prevention

This guide covers everything you can do to resolve and prevent the aF4 over-temperature fault. If you haven't already, read our Blinking LED Guide first for an explanation of what the fault means and how your unit responds.

Step 1 — Power off and let the unit cool

If your unit has not already shut down, power it off and unplug it from the wall. Allow at least 15 minutes for the unit to cool before proceeding.

Do not attempt to restart the unit until you have identified and addressed the cause below.

Step 2 — Identify the cause

Is the unit installed in an enclosed or confined space?

Yes — cabinet, sump enclosure, tight equipment area: Restricted airflow is almost certainly the cause. Proceed to the airflow remedies below.

No — open shelf, open stand, good ventilation on all sides: A faulty over-temperature sensor is the likely cause. Skip to the sensor fix section below.

Remedy A — Airflow issues

The aF4's fan exhausts warm air away from the unit. In an enclosed space, that warm air recirculates and temperatures rise. The fix is straightforward — the unit needs more room to breathe.

Relocate the unit: Move the aF4 to a location with at least 6 inches of clear space around the fan exhausts and intake. An open equipment shelf or the top of an aquarium stand works well.

If you must keep it in a cabinet: Add a small cabinet ventilation fan to actively move air through the enclosure. Passive cabinet designs — even with the door open — trap heat. An active fan pulling fresh air in and pushing warm air out will resolve the issue in most cases.

Clean the fan grill: Dust, salt creep, and debris on the fan grille reduce airflow significantly over time. Before restarting, check the grille for buildup and clear it with a can of compressed air. For a full cleaning walkthrough see our Fan & Cooling System Cleaning Guide.

Once the unit is in a better location and the fan is clean, power it back on, fill the reservoir half way with plain water and check on it after 3 hours. If the fault does not recur, the issue is likely resolved.  To be sure - a run with just plain water for 24 hours should be sufficient.

If the fault returns despite good airflow, proceed to the sensor fix below.

Remedy B — Faulty over-temperature sensor

If your unit is well-ventilated and still triggering the fault, the over-temperature sensor is likely too sensitive and reading artificially high temperatures. You have two options: a DIY fix or a warranty claim.  You will not void the warranty attempting the DIY modification and you can still send it in for warranty if the modification is unsuccessful.

Option 1 — DIY sensor repositioning (no return required)

This fix involves moving the over-temperature sensor from its factory position on the heatsink to a cooler location near the lower PCB. It is straightforward and does not require any specialist tools.

Tools required:

• Phillips head screwdriver
• Hex wrench

Steps:

1. Power off and unplug the unit — ensure the aF4 is fully powered down and disconnected from the wall before opening the housing.

2. Remove the housing — using a Phillips head screwdriver, remove the four corner screws securing the outer housing and carefully lift it away from the unit.  You may have to wiggle it some at the top to get it free.

3. Remove the fan — disconnect and remove the fan to access the heatsink assembly beneath.  Take note of the fan orientation for re-assembly.

4. Remove the over-temperature sensor from the heatsink — locate the sensor attached to the heatsink, secured by two silver screws. Remove the screws and detach the sensor. Once the sensor has been moved, re-tighten the silver screws on the heatsink.

5. Reposition the sensor — move the sensor down to the lower PCB area, away from the heatsink. 

6. Reinstall the fan — reconnect and reinstall the fan.

7. Reinstall the housing — replace the outer housing and secure with the Phillips head screws.  Be careful not to pinch the hoses.

8. Power on and test — plug the unit back in and power it on. Monitor over the next 24 horus to confirm the fault does not recur.

Not comfortable opening the unit? That is completely fine — the warranty claim process below is just as valid an option and results in the same outcome.

Option 2 — Warranty claim

If you would prefer not to open the unit, or if the DIY fix does not resolve the issue, this repair is covered under the aF4 warranty for 13 months from the date of purchase (12 months plus a 30-day grace period).

To submit a claim you will need:

• Purchased from inD Aquatics directly — your order number
• Purchased from an authorized retailer — proof of purchase (receipt or order confirmation)
• All purchases — your unit's serial number (found on the sticker on the underside of the aF4)

📩 Submit a support ticket with the above information and a brief description of your installation setup and the steps you have already tried. Our team will advise on next steps, which will typically involve a unit service or replacement.

Outside the warranty period? Contact us anyway — submit a ticket and our team will assess your options.

Prevention — stopping it from recurring

Whether your fault was caused by airflow or a sensor issue, these habits will help prevent future over-temperature events:

• Maintain at least 6 inches of clearance around the fan exhaust at all times
• Clean the fan grill monthly
• Avoid placing the unit next to heat-producing equipment
• If mounted in a cabinet, use an active ventilation fan

Related articles

• Blinking LED Guide — what the flashing LEDs mean and how the unit responds
• Fan & Cooling System Cleaning Guide — full fan cleaning and maintenance walkthrough

Still having trouble after following these steps? Submit a ticket and our team will help you get it sorted.