I def thought that as well. so i tested with another mobo and then sensor wire for the pwm splitter being plugged in so it should have run at full speed but no dice. the run with no sensor was repeated outside the case with another psu same thing... at the time i thought it was dead until after teardown drain refill and it started back up. tested out of case for 48 seemed fine. installed and tested without power 48 seemed fine. tested with benchmarks worked great. then after a few weeks had to leave the tower without power for a bit and bam no start back up. i remembered the first time i had issue i was moving SSDs on my setup and had left it shut down while working on the other tower before moving back to my main one. . further testing replicated the issue and brings me to where i am now... i can use it fine unless i have to leave my tower powered off for a bit.
I have not really figured out what gets it going .... heat does not seem to do it, as I found out the pump was not working by an alarm i have set for temps hitting 85c on the cpu, (under full load of gpu and cpu never gets close when pump is running).