There’s currently no way for a user to remove such broken devices from their online account/profile, but it should not (ever) interfere with your App and system. If it does ever become an issue for you, then you are perhaps best to speak to Sonos Customer Support via this LINK.

Hope that assists.

Thank you for your response . I replaced the Boost but it's just annoying seeing two Boosts  listed on my system. 

Are you speaking about a notice in the controller that the old BOOST is ‘missing’? I’m not able to test this, but isn’t there an “x” at the right hand end of that notice? 

No. It doesn't say that it's missing...just not connected. 

Is there an ‘x’ in that notice?

That I'll have to check when I am home...I'm presently at work and can't check. 

If you cannot dismiss the message, try to change the Room name to “z”. At least then it will be at the bottom of the Room list. Another possibility is resetting the controller. Nothing critical is stored in the controller. On restart, you may be able to dismiss that message.

I'll give that a try tonight. 

If you go Settings > System > Boost there could be an option to “Hide this product”. Eventually it should disappear on its own but you may be able to help it on its way.

I'll check it out in a couple of hours when I get home. Thanks. 

Ok...you're suggestion was the ticket! Now I won't have to see it every time I open the app! Thanks again!