Niko I will try to answer your original question I don’t have an ultra I have BK insert this is how I determine mine was bad. 8 month old cat died went to dealer exchange no questions asked. Not sure this will work on your stove I noticed my cat wood not light off when up to temp and light off would start at higher cat t/stat setting. At first light stove full looking at cat gauge temperature should rise higher than stove top temperature it didn’t. I then shot stove top above cat gauge then all along across top of stove and temperature was same all the way across looking up at the cat was not glowing. I then ran sooteater to check for restrictions and it was clean. While running the stove (with bad cat)my chimney would puff out black smoke signals.