Oven thermometer only displays lo

What are you using to measure the temperature of the oven? If you using a typical round oven thermometer, the reason is that your thermometer response is slow. It takes about 20 minutes for those thermometers to reach and display the actual temperature, and your oven is probably reaching it's set temperature in about 10 minutes. You really need an electronic thermometer or at least one of those liquid thermometers which you can sometimes find at Ace Hardware or True Value Hardware stores.

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Well, your temp sensors can still be bad. If not, there's always a new control board you buy!

However, I wouldn't drink water from that oasis without making ABSOLUTELY sure I'm not seeing a mirage.

The only common denominators between your upper and lower oven temp readings is the firmware and the oven thermometer you are using to visually check the temps.
What type of thermometer are you using to check your oven temperatures with?
If it's not a digital thermometer used specifically for testing ovens, you might just be leading leading yourself astray.
You need a calibrated thermometer. If I don't have a calibrated digital thermometer on me, I use two or three oven thermometers (the dial type) and average the readings.
It's the only way to be as close as possible with a digital probe.

If you have thoroughly verified that your oven is in fact not reading the correct temperature, then you can adjust it +/- 35 degrees F via your oven's control panel.
To adjust the oven temperature:
1 - Press Setup pad.
2 - Select the down arrow to scroll to the next screen.
3 - Select Temp Adjust using the Quickset pads.
4 - Select upper or lower oven (select models).
-"Set temperature offset using the Upper Set Knob" is displayed.
5 - Enter the desired temperature change using the Set knob.
The temperature can be increased or decreased up to 35 degrees.
The temp. change is displayed at the top of the window.
6 - Press the Set knob to accept the change.

Now, if you are still worried about the temp. reading being off, replace both the upper and lower temp sensors. That's all you can do besides replace the main board.

Temperature Thermistor is bad

It's probable that it needs a new lens filter or the filter needs cleaning. I have no idea how to remove the filter but it probably clips or screws off the bit that goes in the ear.
Quite frankly the device is at best unreliable, it measures infra-red in the ear, great in theory but not very reliable in practice. I would use a different thermometer.

as long as your measured temperature is within 15-25 degrees of shown temp, then it should be ok. remember the temp in the oven will be different from top to bottom.

The thermometer that hang on rack are Whooly inaccurate. A good one is the TAYLOR brand. As long as things bake within recipe time no adjustment needed but to do it;

1. Press BAKE
   
   
2. Select the maximum temp. depending on model it either 500 or 550
   
   
3. Quickly (within 5-seconds of setting 550) press and hold the BAKE button approximately 5-15 seconds until "00" or the previously entered temperature adjustment is displayed.
   
   Pressing longer could cause an F0, F1 or F7 error to be displayed.
   
   
4. Press the UP/DOWN arrow button to change the oven temperature in 5° increments to a maximum of +/- 35°
   
   
5. Press the CLEAR or OFF button to return to normal operation.

But before doing that i suggest a new high quality thermometer that you hang on oven rack

My outside display stopped working, but the inside display still worked. I found that one of the two batteries in the inside unit was almost all the way dead. Once I replaced both batteries the outside display worked. I also checked the batteries in the outside unit. After all batteries were installed, I pushed the small button that is inside the battery compartment on the outdoor unit. It's now working perfect..

does the display go to 425 or are you putting a dial thermometer in it?is the new control doing the same thing as the old control?

hummmm this sounds similar to what is happening to me. I am praying someone will have a solution, I don't want to have to explain to my daughter who is going to be 4 tomorrow, why I can't bake her cake.