Samsung oven immediately shows oven has preheated to desired temperature

[RF_Burns]

We have a Samsung NE58F9710WS split cavity (upper/lower removable divider).  When setting the top level, the oven will immediately BEEP that it has reached the desired temperature, which of course it has not.  There are no codes displayed.  I measure the temperature sensor and it reads 1049 ohms which the Service Manual thermistor chart show is room temperature, (the bottom cavity sensor reads exactly the same).  From the Service Manual there is a code for the thermistor reading way too high or too low, but no code shows.

Prior to this, the oven would reach operating temperature but would not maintain the temperature.  ie, checking the food 20 minutes later and it was evident it was not cooking.  Re-entering the temperature would show the oven temperature had dropped from say 425F to 200F.  The control circuit knows the temperature is low because re-entering the temperature it would then go into preheating mode and show the lower temperature.

I changed the 3 large 40A relays (Broil, Double and Bake) as I do every year thinking the Broil or Double relay contacts were burnt AGAIN!.  I changed them to 50 Amp rated relays this time hoping for a bit longer life from them!

It's been randomly doing both these issues for a bit, but now it seems to be continuously not preheating.

Any ideas?

Thanks,