DIAGNOSIS That’s the battery protection mode. The battery has gotten too low or too hot, and the vacuum is shutting itself down to prevent damage.
FIX First, just let it sit for a while to cool down if it’s warm. Then, plug it into the charger. Don’t use the wall-mounted dock for this—plug the charger directly into the vacuum body. You need to see a solid blue light, not a flashing one. Leave it charging for at least 3.5 hours, even if the light goes out sooner (it will). After a full charge, press and hold the power trigger for 20 seconds. If it runs, you’re good.
IF THAT DIDN’T WORK The battery itself might have failed or developed a memory issue. Try a ‘hard reset.’ With the vacuum OFF the charger, hold down the power trigger for 20-25 seconds. Then plug it back in for a full charge. If it still just flashes, the battery pack likely needs replacing.
HEADS UP To avoid this, try not to run it until it’s completely dead. Plug it in when the power starts to noticeably drop. Also, storing it on the dock in ‘standby’ mode all the time can slowly drain the battery—it’s better to take it off the dock once the light goes out.