@Goatboy Following on from this I can now see it is a widespread issue. This is not a true mesh system and is not fit for purpose. I have requested a refund from Amazon and will be returning. One day of frustration was enough for me, let alone years that some of your other customers have had to endure. 

@TP-Link_Deco Thanks for the response. When I first set it up, I did noticed the 3rd was connecting to the 2nd and I was getting extremely fast speeds all around the house. Then I needed to undo the set up and start again.
It was then I noticed it was only defaulting to the main/1st Deco.
Hard-coding it like this with a threshold is suboptimal because my home office has the 3rd Deco located in it but laptops etc achieve faster connections by connecting directly to the 1st or 2nd Decos (I switch the 3rd off to test this), and when I connect them to the 3rd Deco that is within touching distance of my chair, they have a slower connection. This is very counterintuitive. 
It is almost is my house is too small to take advantage of 3 Decos.

I have tried moving further away....I have even stuck 2 and 3 next to each other but 3 still looks for 1. 

I have not returned it yet....I have a further 12 days. My advice to you guys would be to keep up the communication and allow the app to choose the preferred source for each Deco.

Thanks


 

@TP-Link_Deco One other question if I may. As of today, if the threshold is exceeded, will the 3rd automatically switch to using the 2nd as the source?

@TP-Link_Deco I probably should not have started again. The reason why I did was because I was not sure I had selected the correct Deco model when I did the set up.
Yesterday, I did the following.
I moved Deco 3 as far from Deco 1 as possible (in fact I only moved it about 1.5 metres because I could not move any more).
I moved Deco 2 about 1 metre further into centre of the room on the floor below Deco 3. Again, I was limited on distance due to cable length etc.
I then rebooted Deco 3.

It connected to Deco 2 upon start-up and has remained connected.

So I think your point about threshold is the key here. 
The Decos default to 1 if it's within acceptable range. I suspect in a very large house, they would not behave like this and behave as customers want them to.
I still think adding the flexibility in the app to select source would be a good addition. I believe other mesh systems offer this.

Will Deco 3 remain connected to Deco 2 forever now or if the signals fluctuate, is it possible it could look for Deco 1 again?

Is that how the system works or is it hard-coded to stick to the original paired Deco?

Thanks

@TP-Link_Deco I had the problem of the master connecting with 2 and 3. I wanted 2 to connect with the master and 3 to connect with 2 because of the week signal on 3 as a result of the distance of 3 from the master. This may sound crazy but  I put a metal cooking pot over the master  and  3 immediately connected with 2 which now had a weak signal. I removed the pot and everything was connected in line with good signals. 

@TP-Link_Deco When will this supposed firmware change be released, I have till March 9th to return my Deco s4, on top of not allowing manual channel selection, this issue will be my reason to return if I cannot properly layout my mesh system as needed for my home. This issue was brought up in September of 2020, it is now February of 2021, please provide a more accurate timeframe for "Development".