Reasons for that can be turned statusled

[rimai]

There are only 2 reasons:
ATO or Overheat.

[Sebyte]

I have also found that an intermittent connection on a temperature extension lead plug can cause the LED to come on. One pin had pushed back. It seemed to cause a spike making the RA think it has an over heat. I found this out as my head unit is mounted on the door of my stand and as I opened the door the unit showed the red LED.

Worth checking