Is this your only speaker?

LED meanings here: https://support.sonos.com/en-gb/article/sonos-led-lights

How exactly did you try to reset, and what happened?

What did Sonos support actually say? 
What changed before it stopped working - have you changed your network credentials?

Warnings against a factory reset are given here - but there’s a link too for instructions. Note that for older devices the reset process can take longer, and doing it whilst Ethernet connected can be beneficial. 

No, I have another play 1 that I use for surround sound, a beam and a one.
All of these work, only 1 play1 does not work. 

I tried resetting it by taking it off the power and pressing the play/pause button. I did it both by connecting it to a wlan ( port 1 and 4) and without.

I even waited up to 10 minutes but it keeps blinking white. 

The network credentials remained unchanged.

Sonos support told me to do what is described above but it has not worked and for the technician there seems to be no alternative solution. It is to be replaced.

I, however, would not like to do that and hope for further help from you. 

Odd then: one day it worked, the next it didn’t. Do you have Auto update enabled - was your system updating? If not, it does suggest a hardware failure. 

The reset process is a “press-and-hold” process, per the link in my earlier post - step3. Have you followed those instructions? 

I know it's strange, too :(

I programmed the updates as automatic.

I followed step 3, also suggested by you, but the change from the color white to orange never happened.
 

You need to follow all steps - I was drawing your attention to the need to hold the button, as detailed in step 3. 
Does the white light keep flashing all through the reset process? 

Also, did you read all the article I linked to, including this: 

https://support.sonos.com/en-gb/article/sonos-product-shows-continuous-flashing-white-light-after-updating-to-15-6

Are you Ethernet-cable-connected as I’d suggested?

All steps were followed according to the reset procedure and tried several times but without success. 
The lamp continues to flash white without ever changing color. 

Which button are you holding?

And again I’ll ask: are you Ethernet cabled?

I’m holding play/pause button.

Normally all my sonos are WiFi connected. The play1 that doesn’t work I’m connecting to Ethernet cable following the procedure:https://support.sonos.com/en-gb/article/sonos-product-shows-continuous-flashing-white-light-after-updating-to-15-6

Unfortunately it doesn’t change anything 

In that case next step according to that article is speak to Sonos support. Hopefully, you’ll get someone different to speak with this time. Let us know what they say and how it goes. 

Last update: 

They cannot do anything and therefore offer me a 30% discount for a new product.
I would have preferred to fix it but unfortunately that is the way it is. 
Thanks anyway for the help. 

Thanks for the update. What will you go for to replace it?

I don't know whether to replace it with another used play1 or go to a newer product: Era 100.