my roomba i3+ just has a solid red light and won't start, what's wrong?

Diagnosis

The solid red light ring on the iRobot Roomba i3+ is a general "Critical Error" indicator. Unlike a flashing light, which usually suggests a minor obstruction, a solid red ring means the robot's onboard diagnostic system has detected a hardware failure or a complete blockage that prevents the motor from spinning. This is most commonly triggered by a "stalled" motor in the main cleaning head or the side brush, or a failure in the vacuum's communication with the Clean Base. The root cause is typically an overload of the circuit. If a piece of string, a thick rug tassel, or a clump of pet hair has wound tightly around the brush roll, the motor draws too much current and shuts down to prevent the motherboard from frying. Alternatively, if the robot is stuck on a "cliff" or a high threshold, the cliff sensors may trigger a red light if they are obscured by thick dust, making the robot think it is permanently perched on an edge. To confirm the exact failure, you must trigger the voice prompt, as the red light itself is a generic warning for multiple distinct hardware faults.

How to Fix It

To resolve a solid red light on the i3+, follow this precise sequence to clear the error and reset the system:

1. Press the CLEAN button once. The robot will announce the specific error (e.g., "Error 15: Please clean the extractor brush").
2. If the error is brush-related, flip the robot over. Press the two tabs on the side of the multi-surface rubber brush module to pop it out.
3. Remove both green rubber extractors. Use a pair of scissors to cut away any hair or threads wrapped around the ends of the rollers, specifically around the plastic end-caps where hair tends to bunch and cause friction.
4. Check the side brush (the small spinning brush). Pull it upward and off the post. Remove any hair wrapped around the hex-shaft.
5. Inspect the bin. Remove the dust bin and check the filter (the white pleated fabric). If it is grey or clogged, tap it firmly against a trash can or replace it. A clogged filter creates backpressure that can trigger a red light.
6. Perform a "Hard Reboot": Press and hold the CLEAN button for exactly 20 seconds. The light ring will swirl; release the button and wait for the robot to reboot completely.

If That Didn't Work

• Clean the Cliff Sensors: Use a dry microfiber cloth or a cotton swab dipped in isopropyl alcohol to wipe the six semi-circular windows on the bottom perimeter of the robot. If dust buildup mimics a "cliff," the robot will refuse to move and show a red light.
• Check the Clean Base Contacts: If the red light appears specifically when docking, inspect the two gold-plated charging contacts on the bottom of the robot and the two pins on the Clean Base. Use a pencil eraser to scrub away any oxidation or grime that prevents a clean electrical connection.
• Inspect the Bin Door Seal: Ensure the bin is clicked fully into place. If the bin door is slightly ajar or the seal is torn, the vacuum cannot create a seal, which the i3+ interprets as a critical suction failure, triggering the red light.
• Clear the Vacuum Path: Check the intake port (the hole where the dirt enters the bin). Use a flashlight to see if a large object (like a coin or a pebble) is lodged in the throat of the vacuum, preventing the brush from pushing debris into the bin.

Heads Up

• Avoid Wet Debris: Never run the i3+ over liquid spills. Moisture entering the vacuum motor can cause a permanent short, leading to a permanent red light that cannot be fixed via software.
• Filter Maintenance: Replace the high-efficiency filter every 2-3 months. A clogged filter forces the motor to work harder, increasing heat and the likelihood of a thermal shutdown (red light).
• Brush Care: If you have long-haired pets, remove the rubber rollers weekly. Hair that wraps around the axle can melt the plastic housing if left too long, rendering the brush module useless.
• Battery Health: If the red light appears immediately after a long period of inactivity, the battery may have dropped below the critical voltage threshold. Leave it on the Clean Base for 24 hours without interruption to calibrate the charge.