AO Smith hotwater heater fails after 1 yr of installation by the builder. We know 5 out of 24 (reported failures) in our neighborhood alone. If under the 1yr builder's warranty - the builder's customer service will fix it but, after 1yr you contact AO Smith. The thermocouple and the thermal controller have to be replaced. The manufaturer is willing to send the parts providing you contact them and a plumber to install the parts. Model GNR 40 serial number 0803T001366 is just junk! It was our experience that the part we not delivered on time as promised by the parts dept.