Oven temperature only gets to within 20-25 degrees of temp. set

Generally the oven temperature will fluctuate as much as 30 degrees above or below the set temperature. The longer the oven is on, the less the temperature fluctuates. If you measure the highest and lowest temperatures readings with a thermometer after the oven has been preheated at least 20 minutes, you should come up with an average temperature somewhere within about 10 degrees of the set temperature. You can calibrate most ovens up to 35 degrees higher or lower if it is off. Any more than that requires replacing parts.

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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

If you are monitoring the oven temperature with an analog style thermometer you may actually be ok, but seeing the thermometers slow reaction time.
Some newer ovens actually do pre-heat beep prior to reaching temp in an effort to conserve eelectricity.
A good home test is to try your oven at several different temps to see if there is any variation in internal temperature. Try it one day on 300, the next at 375 and another day at 450. Give your analog style thermometer time to catch up (usually just about 15 min) and leave it on for a half an hour to see if the temp maintains.
Also Beware of aluminum foil AND THE NEW OVEN LINER MATS as they can alter oven performance bay absorbing and blocking the ovens natural heat radiation and convection air flow currents that happen in all ovens, not just convection models.
Another interesting fact is that older ovens used a thermostat in them that operated much like your thermometer and was very slow to react making the oven typically about 100 degrees hotter than where the customer set it. This was just a fact of life before the advent of electronic temperature management and became noticeable when people began trying to bake older "hand me down" recipes in the newer ovens with less than stellar results.
You can mimic the older oven performance by preheating the oven about a hundred degrees higher than called for and after it reaches temp, re-set it to the correct temperature and put the items in right away.
If you find your temperatures fluctuating ask your servicer to replace first the temp sensor and as a last resort the control board as this part is usually pretty expensive.
Good Luck with this!

The fact that top oven is 100degrees less than bottom is no relation between the two; they are controlled by independent stat controls and if the only way you know if the temp is correct, is to set a temp (such as 350 degrees) and put a thermometer in that oven to see if the thermometer is with in 25degrees of the control settting. You need to do this for the bottom oven as well to see if it is aslo within 25degrees of the setting. then you make adjustments for each unit independently. If the controls are mechanical (knob), then the adjustment is within the control (usually by removing knob and serching for a small screw). If the controls are electroonic, then you need to search the circuit board to see if there is adjstments mounted on the board. Goodluck,Macgivor

The temperature is within manufactures specifications.
By that I mean that the majority of manufactures allow a tolerance of + or - 10 % of the set temperature.
So, in your case, 10% of 350 degrees is 35 degrees, thereby showing that the actual temperature you are obtaining is well within the 10% allowance.
I hope this helps you .

You will need to check the oven calibration using a thermocouple based thermometer(the one you stick in the oven is not reliable). Electric ovens should keep a near constant tempature so if you have it set to 350 the oven should stay around 350 once temp is reached. Now gas ovens are a little different. Most use a on/off thermostat and that means the temp can vary from 320 degrees to 370 degrees to keep an average tempature of 350. So if it is a gas oven you will need to let it warm-up for 10 minutes then start taking the lowest and highest 5 consectutive readings. Then add the 5 reads together and then divide the number by 5 and it should be within 10 degrees of the set tempature. If it is off by more than 50 degrees then you might not be able to get it back to proper calibration. The calibration methods are different for each range and depend on the type of thermostat you have digital(push button controls) or manual(knob). The owner's manual for your range might contain the instructions or consult the manufacture's website for the instructions.

From the symptons you describe, I would say that the oven thermostat is faulty, and in need of replacement.
Make sure your thermometer is o/k by checking it against another one, or boil some water, and check the temp of the boiling water, this should determine if your thermometer is o/k.
Hope this helps.

Temp probe/thermometer inside oven dirty, or off attachment, or defective. On some models, a small screw head adjustment is provided to calibrate thermometer under dial knob. Else, I would just set dial 50 degrees higher rather than expense of new thermometer or dial.

You may not need anything. Most people test their oven with a dial type oven thermometer. They are slow to react and often not very accurate. When I test an oven or install a new thermostat, I use a digital thermometer with a remote temperature probe, hanging from the center of the oven, which shows the temp in tenths of a degree. I let the oven cycle on and off at least three times, then take the high and lower readings on the next cycle and average that out to see what the actual oven temp is. Most of the time, if there is a dial type thermometer in the oven it is very slow to react. After 3 to 5 cycles, they often show close to what the actual oven temp is, but the only way to know for sure is to use the more accurate digital thermometer. Most ranges with digital displays can be adjusted + or - about 35 degrees. Check your users manual for this info, but don't mess with it until you have checked the oven with a digital thermometer! Please don't bother rating this solution, as anything but a Fix-Ya drops my score. Thanks.

Take your temp knob off and look in the center of the stem and you should find a small set screw. Using a small precision screwdriver, turn the screw until you see the light come on. (You won't have to turn it far.) Turn it a little at a time, maybe a 1/16 of a turn. Leave your thermometer in the oven with the door closed and at or near the temp probe that is in the oven. This way, you are getting a true reading.