How does a 240v water heater thermostat work?

Answer 1

Most home hot water heaters have both an upper thermostat and heating element, and a lower thermostat and heating element. First the upper stat and element come on and then when that section of the tank is hot enough, the upper stat switches power off to the upper element and sends power down to the lower stat and element. At this point the lower section of the water tank warms up to the setting on the lower stat. (Both stats should be set the same, typically around 130 degrees. This results in about 120 water delivered to the taps, a safe setting. Use a meat thermometer in a glass to test at the taps. Let it run several minutes to allow the home piping system to come up to temperature.) Once satisfied, both elements are then off until one of the two stats decide that the temp is low enough to switch on again, depending on which section of the tank gets cooler faster. But once the upper stat starts heating again, the lower stat and element must wait for it to finish in order to again receive power for the lower section. Typically a home owner will eventually notice that the water heater cannot keep up with the demand for hot water, which usually means that either one of the stats has stuck or failed, or one of the elements has burnt open and no longer produces heat for its section. Unless you are a professional, it can be tricky to figure out the correct troubleshooting procedure, so it's good practice to simply change both stats and both elements at the same time. The parts are cheap and available at most Home Depot or similar outlets. Be sure to turn the 240 volt circuit breaker off before attempting to service, and sketch out a simple map with wire colors, terminal numbers, etc, so as to get it back together correctly.