Sonos Arc Soundbar F21 Error Code Guide (Real Fixes, Not Myths)

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What This Error Means

Quick definition: On a Sonos Arc setup, “F21” usually means the TV has an internal fault or HDMI/eARC glitch that stops audio from reaching the soundbar. It is not an official Sonos error code.

What’s actually happening: the TV’s HDMI ARC/eARC path is acting up, so the Arc isn’t getting a clean audio signal – you get no sound, dropouts, or the TV flashes F21 while the Sonos just sits there.

If you’re on an LG OLED or similar and you see F21 on the TV screen while using the Arc, the problem is almost always on the TV side, not in the Arc.

Official Fix

  • 1. Confirm where F21 is coming from
    • If you see “F21” on the TV screen and the Sonos app shows no error: this is a TV error.
    • If the Sonos app shows something else (network / unable to play), ignore F21 and fix the app error instead.
  • 2. Hard power-cycle the chain (TV + Arc)
    • Turn the TV off and unplug it from the wall for at least 60 seconds.
    • Unplug the Sonos Arc’s power cable too.
    • Disconnect the HDMI cable from both the TV and the Arc.
    • Plug the TV back in, power it on, wait until it fully boots.
    • Now plug the HDMI into the TV’s ARC/eARC port only, then into the Arc.
    • Last, plug the Arc’s power back in and let it boot.
  • 3. Use the right HDMI port and a proper cable
    • Make sure the Arc is in the TV’s port labeled ARC or eARC. Any other HDMI port will not work correctly.
    • If your cable is old, skinny, or generic, replace it with a certified High Speed / HDMI 2.1 / eARC-rated cable.
  • 4. Fix TV sound settings (typical menu names, exact wording varies by brand)
    • On the TV, go to Settings > Sound / Audio.
    • Set Sound Out or Audio Output to HDMI ARC or HDMI eARC.
    • Turn CEC on (called Simplink, Anynet+, Bravia Sync, etc., depending on manufacturer).
    • If there’s an eARC option, set it to On or Auto.
    • For testing, set Digital Audio Out or HDMI Audio Format to PCM. If that works, you can later try Pass Through for Atmos.
  • 5. Re-run TV setup in the Sonos app
    • Open the Sonos app.
    • Go to Settings > System > [Your Arc] > TV Setup or similar.
    • Follow the prompts so the app re-detects the TV and remote.
  • 6. Update firmware on both sides
    • Update the TV software/firmware from its Settings > Support / Software Update menu.
    • Update the Sonos Arc from the Sonos app (Settings > System > System Updates).
  • 7. If F21 is still on the TV with Arc unplugged
    • Unplug the Arc completely (power + HDMI) and turn the TV on by itself.
    • If the TV still shows F21, that confirms a TV hardware issue (often HDMI / main board), not a Sonos fault.
    • Check your TV’s support site or documentation, or contact their service line. For LG OLEDs in particular, see their F21–F40 documentation and repair options.

The Technician’s Trick

This is what people who fix these every day actually do when the official routine doesn’t clear it.

  • Tech move #1: Full CEC / HDMI reset sequence
    • Unplug every HDMI device from the TV. Leave only power plugged in.
    • With the TV unplugged from the wall, press and hold the TV’s physical power button (not the remote) for 15–20 seconds. This bleeds off the HDMI/CEC junk.
    • Plug the TV back in, power it up, wait until it’s fully at the home screen.
    • Now plug in only the Sonos Arc to the TV’s ARC/eARC port with a good cable.
    • Let the TV sit 30–60 seconds, then open the Sonos app and check if it reports TV audio.
    • After that works, plug your other HDMI devices back in one by one. If F21 or audio dropouts return when you add a certain box, that device is poisoning CEC – leave it off or run it through a non-CEC HDMI switch.
  • Tech move #2: Bypass a flaky eARC with optical (saves the Arc, loses Atmos)
    • If the TV’s eARC/HDMI board is semi-dead and keeps throwing F21, you can usually still get audio out via the optical (TOSLINK) port.
    • Use the Sonos HDMI-to-optical adapter (or a replacement) plus a decent optical cable from the TV’s Optical Out to the Arc.
    • Set the TV’s Sound Out to Optical.
    • You’ll lose Dolby Atmos and some formats, but you’ll get rock-solid 5.1 instead of no sound and constant F21 drama.
  • Tech move #3: Prove it’s the TV, not the Arc
    • Take the Arc to another TV that has HDMI ARC/eARC.
    • Hook it up with the same cable, run the Sonos TV setup.
    • If it works perfectly there, you just ruled out the Arc. The original TV needs a board repair or replacement.

Is It Worth Fixing? (The Financial Verdict)

  • ✅ Fix: Arc is under ~5–6 years old, works fine on another TV, and F21 clearly lives on the TV you own now – replace the HDMI cable, use optical, or pay for a TV main-board repair if it’s reasonably priced.
  • ⚠️ Debatable: TV is older (5–8 years), out of warranty, needs an HDMI/main-board swap that costs more than ~40–50% of a new TV; Arc itself is fine – decide if you’d rather put that cash into a new TV with solid eARC.
  • ❌ Replace: Both the TV and the Arc are old, you’ve got repeated HDMI/audio issues, and a tech quotes big money for board work – at that point, a new TV plus possibly upgrading the soundbar is usually smarter than chasing F21 ghosts.

Parts You Might Need

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See also

Still chasing F-series or smart-home error codes around your setup? These guides go deeper on related gear: