About 3 years back I got a call from a customer telling me his smoke alarms were going off and his house was full of smoke. Turns out that he just had his house painted, and the painter dripped enough paint into the flush button that when dry it caused the switch to stay closed after the button was pushed in. This in turn overheated the 16v xfmr and it melted the varnish on the windings which was the source of all the smoke. How close was it to burning?. Hard to say exactly but it sure looked like it was about to go.
Have replaced more than a few chimes over painted buttons.The nutone $10 ones usually melt the plunger.Maybe if they got the backcharge for this they would learn to be more carefull.Door chime $10 labor $100.The problem in backcharging is some use it to make a high profit from an accident.We don't want the painter charging us $100 to paint that spot on the ceiling we made so usually we don't make a big deal out of that rare time he paints our button.As to a fire i have not seen anything close to that.
Have replaced far more chimes and transformers over our helpers installing them wrong than over painters.How often have you heard,sure i know how to install a chime ?