Unfortunately, I don't think it's heat related either. I can leave my 622 on for an extended period with no problems, even turning it off (i.e. putting it in standby mode) and the HDMI signal will be active when I power it up. If I do a soft re-boot, however, regardless of how long it's been on, the HDMI is inactive and only the HDMI reset option in the diagnostics menu brings it back. I have my fingers crossed that the software download being pushed today (version 4.06) addresses the problem. So far, my 622 hasn't recieved the update.