One thing to keep in mind with any "hand soldered" electronic circuitry, is that small globs or bits of solder can sometimes be dislodge or deteatched with jostling and bouncing around inside the control box. Sometimes they are so smally they find their way out one of the cracks or seems. If a errant bit of solder "lands" in the wrong spot it can temporarily short out or otherwise interfere with the opperation of the machine. The circuit boards in the Tesoro machines have machine-placed and soldered parts but there are a lot of wires that are hand-soldered to controls and connectors so the possibility exists for solder blobs. One thing I always check for when wierd opperation occurs, is to shut the machine off and lightly shake it, tipping up and around so as to possibly dislodge anything lose, and then listen for a tiny "rattle". Some times you can "hear" something instide after shaking and tapping it genlty. I have even had a mounting nut and washer come loose inside a machine once. If you get a metal object floating inside your control box, you need to get it out.
One other thing that commonly happens with wires subject to constant movement and vibration is, if they are rubbing against anything metal, with the constant movement of back and forth sweeping vibration can cause the insulation to be worn down, sometimes causeing a short. If you are mechanically inclined and suspect this could be the culprit, remove the mounting screws to the front panel and carefully pull it away from the control box. There will be a lot of wires conneting it, so proceed slowly. Visually inspect as many as you can, to see if any show signs of wear or if any might be rubbing against bare metal anywhere. I will often simply seperate and move them around some, bend them away from metal and in some cases this simple opperation can eliminate erratic opperation. Now I am not suggesting you void your warranty by doing this, so if you dont feel comfortable by all means send it in and Tesoro will get it working fine, but if you are careful it might save you a few weeks without your machine.