@cacb ..just a guess... the one that heats up is the main deco ? .. atleast thats my case.

@MarkoJ Yes I believe the same, the main Deco gets hottest, but I have not done extensive testing. One other unit that is heavily used is connected with a 20m CAT6 cable. It gets warm, but not terrible. It should be said we have cool temperatures here now only 22C indoors. With higher temperatures inside the problem is more noticeable obviously. 

So I would recommend wall mounting the main Deco, based on my own experience.

@SrDarkWarrior i also have a problem with my DECO M5. it is 25°C so very warm and the unit is getting to  65.4°C (underneath).

I have reported this to TP link support.

At first the advice was  This is the environment operation:
Operating Temperature: 0℃~40℃ (32℉~104℉)
Storage Temperature: -40℃~70℃ (-40℉~158℉)
Operating Humidity: 10%~90% non-condensing
Storage Humidity: 5%~90% non-condensing

So the unit was deemed faulty, even though I have swapped it with another that reached the same temparature.

Now the advice is - I'm afraid that replacement does not help to resolve the overheating issue since due to Deco M5 or Deco M9 Plus'scurrent design, it's possible that Deco units get 50- 63°C. And It confirmed strictly that the Deco could work continuously at a room temperature of 40 °C/104°F according to the test result in TP-Link's lab.

If you still worry about the high temperature on Deco, since a brand new Deco M5, it is recommended to return this Deco unit to reseller, so you could get a chance to upgrade or change other Deco Models to Deco X20 or Deco60 which has a cylinder design, which has a better heat dissipation.

I turn mine off at night but now I am going to send them back as i cannot risk the chance of something happening.

Regards,

Warren.

@WarrenTDO Thank you for your reply on status.. i measured 53 C underneath when i have it on 1 cm spikes.. so there is some room under..  i have yet to test the temp when it is flat on the surface... need just put some board under so that i dont ruin my Hifi speaker anymore that what is has ruined...

Need to check from the reseller what kind of paper they need if i need to return my devices also... as they are some months old now... i have 36 months warranty .. a bit sad story this is.....

br. Marko

@MarkoJ Hello, ive turned mine on its side and it it now only at 51.5°C and i would expect it (because it if a very hot day) to be at least 65°C

I will be sending mine back as i cannot take the risk of the device falling over and then going into melt down.

I just now have to find another product.

Regards,

Warren.

I'll going to return my M9 Plus because all units get pretty hot. Temp registered (thanks to my Covid thermometer) at 129F on two units. I worry it may start a fire since the wooden surfaces where I place them get too hot to even touch. It's too bad bcause I really like them and are super fast when cooled.

It's been three days since installing my M9 Plus and they're still running hot. One unit hits 128F and the two higher 126 F. They are all in air conditioned rooms at 70F with good ventilation. Is there anything that can be done to fix this,?

@CJE i returned my devices.. When you put them on some spikes.. You can lower temp to around 50C. Could not figure any other method.. Unless you unbox it 😁..  Probably Not... Very good product otherwise.. 

But as said still around 50..  You probably would need a Stand or something.. 

Marko

@SrDarkWarrior 

Yes, it does get hot, not just warm,  esp. near the center. The vents are at bottom - heat flows up, not down! Wonder what the heat dissipation engineers were thinking when they designed it? Anyway..

Two cheap, almost cost-free solutions:

1. Slightly elevate the device or hang it freely with DIY technique. Ex. Use an old table top photo frame holder OR place 4-5 pebbles and place the device on it. (See pics). Wall mounts cost money. 

2. Place the device upside down :-) Brings the temperature down to acceptable warm.