U-line CO 2075 refrigerator stopped working, only 3 years old. Service man said it needs new control board. I bought it and installed and still not running. Blinking light has indicated "open thermistor" before I changed the board, so now I am changing the thermistors. I pulled 2 thermistors out of back, but can't get the 3rd one loose. I don't want to pull too hard and rip the wires. Any suggestions? Will this likely solve my problem? Thanks!

Looks like this model is now out of date and I wouldn't trust your service guy. Any service agent will know whether the door switch, thermal sensor or control panel is faulty by simply testing them. I would not have to fit complete parts to isolate the faulty part.
Sounds like he doesn't know how to or wants the job of fixing it.
Try an independant repair service, local one man repair shops tend to give an excellent service.
If you want Currys do a good range of fridge freezers; https://www.currys.co.uk/search?q=Liebherr+fridge-freezer+model+CPEL4813&search-button=&lang=en_GB

https://www.currys.co.uk/appliances/refrigeration/fridge-freezers/bosch?searchTerm=Bosch%20fridge%20freezer

https://www.currys.co.uk/appliances/refrigeration/fridge-freezers/hoover?searchTerm=hoover%20fridge%20freezer

To show just one retailer. There are many more out there. Try and buy locally if you can, you will get a better service I find.

I bought a Philips (Whirlpool) years ago and after 3 years, out of warranty, it packed up. The aluminium heat exchanger started leaking. Not worth repairing.
I now purchase Hoover. They has a 10 year parts warranty.
They are all 15 tears old now.
One gets what one pays for I suppose.

call a service man, it maybe something simple, is better then total price of a new one

Have you tried checking to see if anything else works in that outlet? It sounds as if you have lost power to the outlet.

WELL IT IS POSSIBLE THE SECOND CONTROL BOARD WAS BAD ALSO? A 6 YEAR OLD WASHER IS YOUNG U CAN GET A GOOD 10-15 YEARS OUT OF A WELL KEPT WASHER.

check for a faulty thermostat that tells the board when to run or not . If it is still under warranty have a service inspection done .

Replace the pc board kit. Here is the part to order.

lashing light stating that its too warm .. compressor probably is not running / power is ok or lights would not be on . look for a bad relay . somethes you can here clicking in back.

WE JUST HAD THAT SAME PROBLEM AND IT WAS THE DEFROST BOARD. $50.00 REPAIR...

pencj,
My honest answer is that I have seen this before and in most cases the board works properly after the reboot.
Although you may not have lost power, you may have gotten a voltage spike. I would cancel the service man coming out, (I am a working service man myself) he probably will give you two options. #1 Wait to see if this happens again and if it does happen again soon, the board should be replaced. #2 replace the board now.
My suggestion is to soon go purchase a surge suppressor to plug into. This does not need to be a power strip style. A good quality suppressor that only has one or 2 plug in's or plugs directly into the wall receptacle should do fine. Your refrigerators maximum amp draw is listed on the model # sticker inside the refrigerator compartment.
I hope this helps, supertechks