Direct answer
For the Sonos Sub (Gen 3), model eligibility, battery, storage, network and paired state should be stable. First, record current versions and exact message.
What this covers
- Sonos Sub (Gen 3) (Sub Gen 3)
- Sonos product; Wi-Fi/Ethernet, Bluetooth, voice, home-theater and line-in capabilities vary.
- The specific fault this record addresses: app or firmware update will not complete
What it does not cover
- ×The same symptom on a different Sonos product line, which has its own record and its own cited source
- ×An on-screen error code whose meaning has not been checked against this exact model's manual
- ×Live electrical, gas, sealed-system, internal battery-cell or structural repair — a technician boundary, not a self-service step
Differential
What actually causes this, and how to tell them apart
These are ordered by how often each one is the answer, not by how easy it is to try. The point of the middle column is that two causes producing the same headline symptom rarely produce the same detail — that detail is what tells you which one you have before you change anything.
- 1
The device went out of range or slept during the transfer
What separates it The update fails at a different point each attempt.
How to confirm Keep the phone next to the device, with the screen on and the app in the foreground, for the whole update.
- 2
The app itself is out of date
What separates it The update is not offered, or the app cannot see the device.
How to confirm Update the companion app first; it is a common prerequisite.
- 3
The device is connected to another source
What separates it The app cannot take control of the device to update it.
How to confirm Disconnect it from every other device so the phone running the update has sole control.
- 4
The update is staged and rolling out gradually
What separates it A version is known to exist but is not offered.
How to confirm Firmware rollouts are staged over weeks, so a device can legitimately show nothing available.
Before you touch a setting
Record this first — changing settings destroys the evidence
Every item below stops existing the moment a reset, re-pair or settings change is made. Written down first, they are what separates the causes above; recovered afterwards, they are guesswork.
- The charge level at the time of the attempt.
- Whether it fails at the same point or a different point each time — a different point means an interrupted transfer.
- Whether the companion app itself is up to date.
- Whether the device is connected to anything else.
Keep the phone beside the device with the app in the foreground
ReversibleBackgrounding the app or walking away is the most common cause of a transfer failing part-way.
Update the companion app first
ReversibleAn out-of-date app is a common reason an update is never offered.
Disconnect the device from every other source
ReversibleThe phone running the update needs sole control of it.
Model-specific
What is true of this model and not of its siblings
Generic advice for the product line fails here. Each item below is a property of this specific model family that changes which of the steps above apply to you.
- Model scope
- Sub Gen 3. Sonos product; Wi-Fi/Ethernet, Bluetooth, voice, home-theater and line-in capabilities vary.
- Type — wireless subwoofer (mains-powered)
- A mains-powered wireless subwoofer that bonds to a Sonos soundbar or speaker pair over WiFi to add deep bass. It has no battery and no standalone function — it only works bonded to another Sonos product in the app.
- Bonding
- 'No bass / Sub not working' is usually the bonding: confirm the Sub is added to the same room as the soundbar in the Sonos app and is on WiFi. It must be assigned to a soundbar/speaker to do anything.
- Placement & level
- Sub bass is adjustable in the app; a Sub in a corner sounds boomier. If bass seems wrong, run/adjust the level and Trueplay tuning rather than assuming a fault.
- Symptom boundary
- This record covers Sonos Sub (Gen 3) when it app or firmware update will not complete. A different symptom on the same hardware, or this symptom on a different Sonos product line, has its own record with its own causes and its own cited source.
Stop boundary
When this stops being a self-service repair
Continuing past any one of these costs more than the repair saves — in safety, in warranty, or in evidence a technician needs.
- !Do not power off a device or close the app while firmware is actively writing — an interrupted write can leave an accessory unusable.
Evidence ledger
Sources behind this answer
Visible sources support the visible claims. Home Product Support records the publisher, the fact used and the review date; community reports can suggest an issue but do not become a published fact on their own.
Where the manufacturer's article stops. Sonos publishes this as "Update your Sonos speakers". Sonos' update procedure, including what to do when an update does not complete. Probed 2026-08-21: title-verified. What that article does not carry is the model boundary — it is written for a product line, and Sub Gen 3 is the scope applied here. Where a control label, terminal, indicator pattern or reset sequence differs on your unit, the manual for that exact model is the authority, not this page and not the article.
Exact questions
Common follow-ups
My Sonos Sub isn't producing any bass.+
The Sub only works when bonded to a Sonos soundbar or speaker pair, so first confirm in the Sonos app that it is added to the same room and shows connected. It also needs power and WiFi. If it is bonded and still silent, adjust the Sub level in the app (it may be turned down), check placement (corners boom, open floor is flatter), and re-run Trueplay. A Sub that will not bond at all is usually a WiFi/network issue.
The firmware update keeps failing part-way through.+
Failing at a different point each time means the transfer is being interrupted rather than rejected. Charge the device fully, keep your phone right next to it with the app open and in the foreground for the whole update, and do not let the screen lock. Backgrounding the app is the single most common cause.
Does this answer apply to every Sonos model?+
No. It is scoped to Sub Gen 3. Sonos product; Wi-Fi/Ethernet, Bluetooth, voice, home-theater and line-in capabilities vary.
What should I record before troubleshooting firmware or app?+
Record the complete model identifier, exact message or indicator, software/firmware where visible, the operating stage and what still works.
Why is a factory reset not the first step?+
A reset can erase accounts, networks, maps, schedules or preferences without distinguishing firmware, app. The ordered checks preserve that evidence.
When should I stop and use qualified service?+
Never interrupt an active firmware flash or use unofficial files.
Answer for the exact device and software version shown above.