Rinnai P70EV-714 Thermal Fuse Assy 32e/HD70e - Genuine Spare There are two layers of overheat protection in the Rinnai Infinity 32e and HD70E - a bi-metal overheat switch which you can reset and the thermal fuse assembly, which can't be reset. The fusible link is stuck to the heat exchanger & it's the last line of defence - it only cuts off the power supply if the temperature shoots up to 129°C. By the time it blows, something has gone seriously wrong with your appliance - a really bad overheat condition has gone past the bi-metal switch's safety limit and got past temperature that's so hot it trips the thermal fuse and shuts down the heat exchanger and everything else. The thermal fuses are a one-shot deal - once they're blown, they're done for, and there's no magic fix. You can't reset them, or bypass them, or pretend they never happen