The water heater thermocouple might need to be replaced if it corrodes badly or if it cracks or breaks. Making sure that your replacement thermocouple is installed correctly so that it does its job efficiently. A thermocouple can be cracked or misaligned which will cause trouble later. Here are a few of the most common mistakes you can avoid.
If the thermocouple is cross-threaded when installed into the gas valve it will not work properly. The connection has to be correct in order for the thermocouple to send the proper signals to the sensor.
When screwing the thermocouple into the gas valve be sure to not over tighten it. This can cause the thermocouple to either become damaged or it may damage the sensor in the gas valve. The thermocouple is a coiled brass or copper device and it is very soft metal. The thermocouple can be cracked or broken if not treated with care.
If you do not align the thermocouple properly on the pilot light then it will not do its job. The thermocouple should be aligned with the bulb at the end of the thermocouple right at the tip of the pilot light. If it is not aligned then the thermocouple will not notify the gas valve to open to heat water, or shut off.