You need to turn on the line in initially while the PLAY:5 (or any Sonos speaker, it’s a software switch) is connected to the Wi-Fi, as it is off by default. However, once you’ve done so, you can remove the PLAY:5 from the Wi-Fi connection, and the line in, having been already turned on, will continue to work. 
 

Sonos is a ‘whole home system’, and not just a standard speaker. That means there are some, perhaps unfortunate, requirements. The need to turn on the line in, as well as the 75ms delay, are part of those requirements. 

“If it does have to have wifi whats the point in a line in??” Some people want to connect their CD-player or turntable to Sonos and be able to play Spotify on the speakers without having to cable connect anything. For those people having both a line in and wifi is perfect.

Hi Bruce,

Thank you for your reply, I followed your directions and turned the line in on whilst connected to WiFi and the line in showed connected inthe app. I then discontected from the wifi and have no music playing anymore. Any assistance is greatly appreciated

Cheers

Nicholas

Was Line-In playing when you disconnected the WiFi?

Yes it was, Maybe an idea if I explain what I am trying to achieve, I am going on a four day car trip in my classic car which has a terible old stereo in. I am planning to purchase an inverter to power the play 5 via the cigarette lighter and want to connect to my music to have a decent quality of music for the trip. As SONOS 5 is not bllue tooth I was hoping to use the line in to achieve this.

does anyone happen to know how many Amps of power the play 5 draws

@buzz success managed to get it working on line in thank you for your assistance. 
 

you don’t happen to know how many Amps of power a play 5 draws do you?

While idle: https://support.sonos.com/en-us/article/sonos-power-consumption-while-idle

While running: look near the power socket. It may be printed dark gray on black or light gray on white, but the power consumption is printed here.

I have not attempted to use a PLAY:5 on an inverter. I recommend using an inverter with a “sine wave” output. And, allow a generous margin between the inverter rating and the PLAY:5’s rating.

With respect to your “no WiFi” use of the PLAY:5’s Line-In: Test this at an offsite location prior to leaving on your trip.

Or, pick up a Roam, using the built in battery for power, and Bluetooth for connection. Likely to be much less trouble than attempting to power a PLAY:5 on an inverter. Just be sure to set it up before leaving home, the Bluetooth connection won’t work until after it is set up on your Wi-Fi. In that matter, it’s similar to the line in on the PLAY:5, it needs to be turned on first. 

Choose the Sonos speaker the source is connected to and touch Line-In. On a Mac or PC, go to Manage -> Settings (PC) or Sonos -> Preferences -> Room Settings (Mac). Choose the Sonos speaker the source is connected to from the Room Settings for drop-down and click the Line-In tab.

The Sonos Play:5 (Gen 2) is primarily designed to be a wireless speaker that relies on a Wi-Fi connection to stream audio content. However, it does offer a Line-In feature that allows you to connect an external audio source, such as your iPhone, using the Line-In plug.

When you connect your iPhone to the Play:5 using the Line-In plug, the audio from your iPhone will be played through the speaker. In this scenario, the Play:5 does not require a Wi-Fi connection specifically for playing audio through the Line-In source. The Line-In connection bypasses the need for a network connection because the audio is directly transmitted from your iPhone to the speaker through the physical cable.

The Line-In feature can be useful in situations where you want to play audio from a device that doesn't support wireless streaming or if you prefer a wired connection for better audio quality or stability.

However, it's important to note that while the Line-In connection doesn't require Wi-Fi, the Play:5 itself still needs a Wi-Fi connection to function properly in other aspects, such as setting it up, controlling it using the Sonos app, accessing online music streaming services, and integrating it with other Sonos speakers in a multi-room setup.

So, in summary, the Line-In feature allows you to play audio from an external device through the Play:5 without needing a Wi-Fi connection specifically for that purpose. However, the Play:5 still requires a Wi-Fi connection for its overall functionality and integration within the Sonos ecosystem.