I realize that this is 2012 and a few years have passed since some of these comments had been placed, but after reading thru all of them I have yet to see anyone mention using heat transfer paste when re-installing the heat pipe assembly. I have a Lat D530 that I've (unfortunately) upgraded the BIOS to A10 and of course it has had issues with this very same problem. I just re-assembled the unit after pulling the heat sink / heat pipe out and cleaning everything (including the chips). After making sure everything was clean, I re-applied some heat transfer compound and re-assembled the unit. In my case the problem has been solved - at least for now. I suggest that you DO NOT upgrade your bios to the latest revision unless you are told to do so by DELL. Doing so could could create this issue to come of light.
May the force be with us.
Edit #1 - That didn't fix it! And I was able to downgrade the BIOS to A01. Of course while attempting the downgrade I was warned that this was not a good idea but I did it anyway and the computer restarted just as it should, but with the heat error code. Because I am an experimenter, I will try a different fan assembly to see if this is the problem - since it does not appear to be running.
Edit #2 - That didn't fix it either. So I shall use my little Latitude with LInux for the rest of it's natural life - however long that may be.
I won't replace the main board. I will just part it out when the time comes to retire the unit. Oh well, can't say I didn't try.