I am trying to understand a Rheem 80 Plus. The transformers keep failing. I have been using standard 24v 40va transformers although they are not the factory original. A local service company swapped it out with what he had on his truck. He modified the wiring slightly. Rheem calls for a 24v 40va but one lasted a year and another one lasted three days. Is the 40va simply under sized? I have never heard of transformers failing like fuses before?