I have the same issue as you with a similar model: GDT580SFSS. I have done all the same troubleshooting steps, and have even checked the new control board for power to the heater circuit directly on the board during test mode (removed the heater circuit plug). Nothing. No current.

I located a service manual online for a similar model to mine, that is almost identical in every way. It mentions the thermistor in the troubleshooting steps for the heater circuit. I removed mine (it's located in the flood switch in the inside of the dishwasher), and tested for resistance. The specs were close though not exactly the same as the manual stated. That's the only other thing I can think might be wrong.

Until I saw your post, I was thinking I might have gotten a faulty replacement control board, but now I'm thinking that there must be something else we are both missing. I'm stumped! There's not much more to replace! Like you, I'm really not wanting to buy a new unit. It's frustrating that we can't find better info online.

Here's a link to the manual I found in case you want to check it out:http://pdfstream.manuals...4b-904f-9ff9d039ccd3.pdf

Let me know if you discover anything, and I'll do the same for you! Best wishes for warm and dry dishes. ;)

Well, I ordered the thermistor and installed it today. I immediately ran the heater element test, and sure enough, the element sprang to life. That was the problem all along. $25 part from Appliance Parts Pros. Easy to replace from the inside of the tub.

Hope this works for you too! Best wishes.