Not sure I understand, but you get one discount on an item. They are not stackable. 
 

The discounts are always on MSRP, not the ‘sales/marked down’ price. 

I understands that for one product I will get 15% and they are not stackable.

the question is only if i get 15% on my old sonos play 1, can i use this credit to buy sonos sub (gen 3) or only e.g. new sonos one smart speaker

You can use it against any product. At times in the past the discount could be used against specified bundles of speakers but I don't know the current position. 

You will have to upgrade from S1 to S2 to use a Sub gen 3 so you may wish to use the Bridge upgrade credit to get a Boost.

If you select the Sub (gen3), which is currently discounted at a price of $599.00 - then you get it at that price. You can’t use the 15% discount on top of the current sale offer.

However, the Sub-Mini, which is not part of the seasonal offer, can have the 15% discount voucher applied to it - also the speaker ‘sets’ that are not in the seasonal offer, will be treated as one purchase item, so you could get 15% off the entire speaker ‘set’... so maybe look to spend your trade-up discount voucher wisely.

So please take me through this example..…

I have x1 Sonos 5, x1 Sonos 3, x3 Sonos 1 (all old S1 app based).

Can I recycle these speakers with you and get credit from you to use towards spending on new Sonos speakers, regardless of model?

Note, this is a ‘user’ community and any Staff here are clearly identified. I’m just a user, not a Sonos employee.

The device types you mention, am I right in thinking you are referring to:

• Play: 5 (gen1) -
• Play: 3
• Play:1

If those are correct, then ‘Yes’ you can trade up all those products.

If you go HERE and login to your Sonos account you will see the trade-up offers open to you, by selecting the UPGRADE tab/menu option.

Hope that assists.

edit: Also see this link…

https://www.sonos.com/en-us/upgrade

Absolutely correct. These are those speakers. Thank you for the link. I just want to ensure that I perform the steps for this upgrade correctly, because I am looking to recycle my old speakers via Sonos themselves and whichever upgrade programme they offer. 

Note, although you needed to ‘recycle' them for a while,  now you get the upgrade discount but keep the devices used to get them - and they carry on working just as they do now.

Hi @sjw  Thank you for your reply, but I'm not sure I follow. Wouldn't I need to send my old Sonos kit back to Sonos to get the credit towards the next purchase? When you say "keep the devices used to get them" I was just wanting to fully understand what you mean. Cheers.

No, you don't need to return them, it's as I said above. They're not bricked or anything, you can keep them and use as you wish.

@sjw is correct @BennyBoy you can trade up your speakers, but still hang onto them and continue to use them - if you do sell them on, then let the buyer know you’ve used the upgrade offer, so that they are fully aware of what they’re purchasing.

I just gave my old Play:5 & Play:1 devices to family members to use in their Homes.

@Ken_Griffiths and @sjw - Thank you both very much for your help. I very much appreciate this. This sounds great. Will go check this out as I registered my speakers with Sonos when I first got them. Will post here how it goes.

Check here - it should list your speakers and any upgrades available.  Lower down shows Upgrades already ‘claimed’.  (you will see a ‘shipping label’ link too.  Don’t worry, you don’t need to use it - that’s if you wanted Sonos to dispose of it for you - which I can’t imagine anyone using now)

@sjw - Yes thanks. I can see all the stuff available for upgrade. Sonos have it set so you can only either get the current discount on offer, OR only apply the upgrade credit, but not both. I saw this at the checkout basket. (I think this was mentioned earlier on in this chat thread).

No worries. All is not lost... Just seen I have some Amazon gift vouchers and also found the speakers I'm looking for (new) at a decent price. To end it all, I'll still have my old working Sonos speakers and may give them to my family.

Once again, many many thanks for all your help. Best wishes to you all.

Aren’t Sonos offering 20% discounts at the moment?

This might be only in the United States.

Nope; UK too. 
 

Yes, they remind a few times a day...

Yes correct. Even cheaper on Amazon UK, for the Sonos SL Ones so I see.