iRobot Roomba · updated 2026-07-06

Error 21: Mobility board communication lost

What it means

The main computer lost communication with the mobility board.

The fix

Restart the mission; if it recurs, reboot the robot.

Applies to

i Series

Source

Official iRobot support article: https://homesupport.irobot.com/s/article/2413

Fix didn't take? Charging-family errors that recur usually mean the battery — see the charging-errors guide. For anything deeper, here's who actually repairs Roombas in 2026, with published prices.