Purchasing a water heater thermocouple is going to involve a trip to the home supply store or some time on the internet. You have two choices when trying to purchase a thermocouple. One would be to find an original equipment part (OEM). The Second option (the likely option) would be to find a universal thermocouple that will fit your water heater.
Not sure if you need a new thermocouple? See the article 'Troubleshooting Gas Water Heaters' for more information and a coplete listing of all of the gas water heater topics. After you obtain a new thermocouple you will need to install it. See the articles 'Removing a Thermocouple Assembly' and 'Installing a New Thermocouple' for information and instructions.
The information below will help you to determine what information you need to purchase a new thermocouple that will work for your water heater.
Thermocouple or Thermopile Description
Simply put, the thermocouple or thermopile as they are sometimes called is a temperature sensor. For safety reasons, the gas valve will not allow gas to go to the manifold unless there is a flame at the pilot to ignite the gas.
A thermocouple uses two types of metal to create an electrical current that the gas valve can sense. If the electrical current is transmitted, it means that the end of the thermocouple is hot and there is a flame. Simple right? Don't go looking farther than this for an explanation, this stuff can get pretty techinical.
In practice, the thermocouple looks like a copper wire with a thick section that has a sensor end and an end with a fitting that goes into the gas valve. From an operational perspective the thermocouples for a water heater are all pretty much the same. However, there are two variables, the length and the fittings used to install them, see below.
A failing thermocouple will not send the correct electrical impulse and the gas valve will not release any gas. When this happens, you do not have hot water.
Thermocouple Part Numbers
Hunting up part numbers for water heaters can be a daunting task. First there are so many brands and models out there. Some of the better brands have websites that let you look up information, but as a rule, these websites are not do it yourself friendly. When it comes to specific information that is needed to make a repair, they are very vague.
You may think that looking in your manual and finding a part number is all that will be needed to solve your problem. Find the part number and order a replacemnet. The trouble is that most manuals do not list the individual part numbers for the thermocouple.
Instead, the parts diagram will show the entire manifold as a part. Replacing the whole manifold is an option, but why would you spend the extra money when all you need is the thermocouple or thermopile that costs less than ten dollars?
Some manufacturers do have 'name brand' thermocouples available. They may provide a manufacture date range or model range for which water heaters they can be used on. These will cost more as a rule and can be a reasonable option.
Universal thermocouples, as the name implies work on most water heaters. They are available online and in home supply stores for a reasonable cost. The length and the thread type are the two concerns when purchasing one.
You are going to want to take the old thermocouple with you to get a replacement. A couple of things to watch for. You want to get one that is about the same length as the one you have. They are sold in in 6" increments for the shorter lengths, 18", 24", 30" and so on. For a water heater, 18" and 24" are common, although longer ones are possible.
Remove the old thermocouple and measure it to see what length you need. Try to get as close as you can to the original. You cannot cut them, bend or kink them, but you can coil them if needed. The length of does not affect how they work.
You may wind up with a thermocouple that is longer than the one you have. You can add a loop or two the make it work.
Thermocouple Thread Types
Left Hand or Right Hand Threads
Many gas valves have a left handed thread where the fitting for the thermocouple goes. You need to make sure which thread pattern you have before you order the new thermocouple. Don't plan on trying to make one work that is the wrong thread.
They make and adapters that will allow you to use a standard thermocouple on either a left hand or right hand fitting. A plumbing supply store should have the adapters available.
Most 'Universal' thermocouples include adapter kits along with the thermocouple. This is the best choice in most situation. The package will contain a few different fittings that can adapt to either left hand or right hand thread. Usually, thay also include a couple of different retaining clips for the sensor end of the device.
You can find 'universal' thermocouples on line for under ten dollars. Most of them include an adapter kit that allows you to install it on most water heaters.
You can pay upwards of fifty dollars for a 'name brand' thermocouple. These will not have adapter kits, so you need to make sure you are getting the right one for the make and model of the water heater you have.
Thermocouples are an inexpensive but important part on a water heater. If you have time, you can order them online. Keeping a spare handy is not a bad idea. You can also find 'Universal' replacement thermocouples at home supply stores.
With your new thermocouple in hand, you will need to install it. See the articles 'Removing a Thermocouple Assembly' and 'Installing a New Thermocouple' for information and instructions for this task.