My oven has had three thermostats fitted recently and an oven thermometer is regestering about 50 degrees cooler. what cani do?

Question edited for clarity.
Question moved to Thermador.

This says the adjustment is behind the control knob.

https://www.justanswer.com/appliance/1o2k7-calibrate-thermador-oven.html

Videos here. You may need a new thermostat.

https://www.google.com/search?q=Thermador+PRG305PH%2F02+calibrate+oven+temperature

..

If you are certain your oven thermometer is accurate and the oven thermostat is electronic there might be a calibration adjustment a service engineer could make.

375 does err on the safe side. An oven is not an industrial furnace and so being built down to a price usually has certain quirks - hot parts and cooler parts and housewives (and others) usually take great pride in "knowing" their own ovens just as a shooter knows his rifle and will soon unconsciously begin to compensate for a sight that is "off".

Has this just happened or have you suddenly just tested the oven temperature with a RELIABLE thermometer? Some cheaper thermometers can give a false reading. Check with a accurate thermometer first and place it at intervals in different parts of the oven ( it does vary) and take the average

Sounds like you need a new oven thermostat or get an oven thermometer and by experimentation draw up a new heating range for the oven dial.

There is a calibration method to adjust the oven thermostat plus/minus 35 degrees if it is a digital display. The method varies depending on the model range. This calibration method is used to adjust the thermostat if it is not keeping proper tempature. For example if you are setting the oven to 350 and the actual temp it is keeping is 325 then you could use the calibration method to adjust it plus 25 degrees to correct the temp. Just so you know electric ovens will keep a pretty even temp but gas ovens will vary by 40 or more degrees to keep an "average" temp. For example the burner will come on when the oven is 330 degrees and turn off at 370. 330+370 then divide by 2=350. So a oven thermometer may not show you the temp you set it at in a gas oven but does not mean the oven temp is off.

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.

next to last page in your manual


Adjusting Oven Temperature
Oven temperature has been factory calibrated and tested. If
oven consistently over or under cooks food, adjust thermostat.
Oven temperature can be increased or decreased 35°F. To
avoid over adjusting oven, move temperature 5°F each time.
1. Push BAKE pad.
2. Press + pad until an oven temperature greater than 500°F
shows in display.
3. Immediately push and hold, approximately 5 seconds,
BAKE button until “00” appears.
4. Press + or - arrow pad to adjust oven temperature.
• To increase oven temperature (for a hotter oven), Press
pad until a positive number appears in display.
• To decrease oven temperature (for a cooler oven),
Press pad until a negative number appears in display.
5. Press OVEN CANCEL pad to save adjustment.
• Setting is saved if power fails or is disconnected.

heres a link to the entire manual if needed
http://shop.amana.com/assets/pdfs/literature/32103601.PDF

I'm not sure what properly means.  If the unit is working, you can get a cheap oven thermometer to check the function of the thermostat.  Let the unit come to 350 and check the thermometer.  If it is off by more than about 20 degrees, there is a calibration change method in most oven handbooks.
If the unit is not working at all, this is another issue and needs a different set of diagnostics.

you might have already thought of this, buy an oven thermometer you can pop in the oven.
I bought one from my local cook shop
I have a the same cooker and similar problem - mine gets hotter by 50 degrees so I set the temperature 50 degrees lower than needed.
I noticed the problem a few years a go and luckily hasn't got any worse.

maria