I've just finished putting together my custom build, everything seems to be running ok except the CPU is running at 80'c when idle, which obviously is waaay above the temp it should be.
I've got a water cooler system, 2 top fans and and the regular back fan, as well as obviously gpu fans and psu fan etc. I've also got the front of the case slightly open just to let a little bit more air in.
System specs are:
Operating System: Windows 10 Home 64-bit
CPU: AMD Ryzen 5 2600
RAM: 16.0GB DDR4
Motherboard: ASUS PRIME X470-PRO
Graphics: 8176MB ATI Radeon RX Vega 56
Monitor: Acer RT280K (3840x2160@59Hz)
Storage: 931GB Seagate ST1000DM003 (SATA HDD)
Anyone have any ideas why it might be overheating like this? It's my first ever build so it might be a dumb simple thing so don't worry about suggesting basic things :')
I've gone through cable management and dust removal with it being put together so recently so can rule these out. I've also not overclocked anything.
What is the Make & Model of your CPU Cooler?
First make sure it is installed correctly with the part that sits on the CPU is making a tight connection on the CPU surface (Pump). If the pump is not properly screwed down on the CPU it will not be able to cool the CPU properly. You might be able to check this by turning on power and carefully pressing down on the pump connected to the CPU and see if the temps go down. If it does, this indicate that the pump is not seated properly and tightly on the CPU.
Note: there was another thread with the same problem as you on a Ryzen 2xxx processor here at AMD Forum Processors. Turned out the User didn't screw down the CPU Pump tightly because he was fearful it might damage the CPU or motherboard. Once he screwed it down and secured it tightly the temps returned to normal for the liquid cooler.
The User's Processor had the same TDP (65 Watts) and Maximum Operating Temperature of 95C as your processor. So a liquid CPU Cooler should keep the Processors temps below 80c while under load conditions not idle.
Feel the input and output hoses from the radiator. One should be slightly warmer than the other plus you should feel a liquid being pumped from the CPU.
Check for any blockages or leaks from where the hoses connect or if you don't feel the liquid moving in the hoses.
Make sure the Radiator Fan and Radiator is not blocked in any way that may interfere with the Air around it from cooling the Radiator or fan circulating the air around it.
Kinda looks like the pump isn't running normaly with temps that high at idle (check the pump hoses, it should be warm and not too hot), if you have the pump connected to the cpu or pump header, check that its connected securely and is being detected properly in the bios, also check to make sure its running at 100% in Auto or DC mode.
If everything checks out in the bios, check that your CPU usage is normal at idle (Task Manager should show only 1% utilization at idle) as there's recently been a nasty windows10 bug that came with a recent update that affects a number of 1903 users that hasnt been officially fixed yet that keeps your cpu usage high at idle, one of workstation i was working on was affected by this bug and CPU usage was constanatly 10% to 60% no matter what you did.
Also you didnt mention what type of Case you were using and your full fan setup (and type of thermal coumpound used) since you didnt mention having any intake fans, only 3 fans on an unkown config (intake or exhaust). I'm guessing the Rad is mounted at the Case intake and the the three fans are all exhaust maybe? if so check that the case is getting enough Airflow as too much negative pressure will add to the heat your CPU is getting.
and there can never be too much thermal compound, only too little. too much is when you the compound is starting to spill onto your AM4 socket.