DIAGNOSIS A blinking red light on the sub means it's lost its wireless pairing with the soundbar. This is almost always due to interference or the sub being placed in a bad location.
FIX First, let's re-pair it properly. 1) Unplug the subwoofer's power cord from the wall. 2) On the soundbar itself, find the small button labeled 'ID SET' on the back or side. Press and hold it for a few seconds until the display shows something like 'Start ID Set'. 3) Now plug the subwoofer back in. It should automatically search and connect. The light should go from blinking red to blinking white, then to a solid white. Don't move anything until it's solid.
IF THAT DIDN'T WORK Interference is the culprit. The wireless sub uses a specific frequency that can get clobbered by other electronics. Move the subwoofer to a spot at least 3 feet away from your router, cordless phone base, microwave, or large metal appliance. Even a power strip or surge protector can sometimes cause issues—try plugging the sub directly into a wall outlet.
HEADS UP Thick concrete walls or floors between the soundbar and sub will kill the signal. They need a relatively clear, unobstructed path. If you must have the sub in another room, this wireless system probably won't work reliably for that setup.