What caused it to stop working?

Sometimes they have a external fuse which is close to where the wire goes in.

Or, the element has failed. Do you have a digital multimeter? Both items are easy to test.

Or it may have a thermal fuse, again an easy test with a meter.

https://www.google.com/search?q=DeLonghi+Alfredo+toaster+oven+XU21+ST+suddenly+stopped+working+after+baking

Videos. The make is not important as they all work the same and are all made by the same factory in China.
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Probable heating element or control failure

Hope it can help you!

https://www.youtube.com/watch?v=0H_2xkHX2MU

Hola, lo m?s seguro fue que se da?? la resistencia (lo que haces que caliente) tendr?as que mandarlo a revisar con t?cnico

This is caused by a bad contact on the heat sensor located on the top inside the oven...now if i could juste find the replacement part...

Having a toaster oven and a coffee maker on the same circuit is asking the breaker to trip in the house electrical panel, but I guess that you have learned the drill: only one appliance on at a time. Try moving the oven to the working side of the socket (the two socket sections can be spit apart and power each half from a separate house breaker and wiring). If the oven now works, check for a tripped breaker in the house panel. If the oven still doesn't work, look for a reset button near the cord entry point. Many heating type appliances have a thermal fuse that opens when things get too hot, but you need to get inside the cover where the cord enters.

this is all to common . what thought happend did happen . the control board went bad and the elements where stuck on . inside there is a thermal fuse ,it blew out and saved you from haveing a fire but now the oven is dead . if you replaced the fuse it would just do it again and the board cannot be bought so your out of luck . on your next oven stay away from electronic controls . i am shocked you got 3 years out if it ,most go bad mutch sooner

Hi budluco
Happy to help you!!
This is very dangerous and could hurt someone or cause a fire!
Unfortunately if this oven is that old you can buy a new one for the same or less than repairing it!

I am happy to assist you!
Neil

PS. Before you leave this site please leave a "Problem Solved" rating for me on fixya.com

The contacts for these toasters fail. The plasic cam that depresses the contacts also can melt. The design is poor and no replacement parts are available. When selecting a setting, if the selection is not exactly perfect, the contacts arc and eventually fail. Unless cuisinart changes the selection cam to a solid state or relay, this failure will continue to happen during normal use. If your unit works properly do not switch the function setting while heating, this will cause the contacts to arc and erode the contact surface. This posting is applicable to the TOB-30BC, TOB-30BCC and probably all TOB-30XXX models.

With mine, the toaster function stopped working. The light lit, but the relay did not click. This happened about a year ago, but then it started working again. Now that my waranty expired, it seems permanent.

The relay requires 12V, but I only measure 5V (no audible click). When I pulled the relay, the drive went up to 12V, so the coil is loading down the source. Not sure whether the problem is the coil or the source. It would be nice to find a schematic. When I put the relay across a car battery, I heard the click indicating that the relay is working.

I cleaned the contacts, and get the same result.