I used an hovabator for a couple of years to hatch gecko and tortoise eggs, unfortunally it suddendly had a problem with the waffer thermostat and cooked 10 sulcata eggs. Personally I do not trust those incubators.
Replacing the waffer thermostat on a yearly basis is for precaution porpouses and of course it is not necesary mean that if you do no do this, your incubator is going to fail.