Usage:
A very high percentage of jacket water (insertion type) heaters that have been returned from the field have a single failure cause: they were not fully surrounded with coolant. Electric jacket water heaters have a very high heat output for their size. This means that coolant must fully surround the element in order for this heat to be removed from the element. Because these heaters have no thermostat, failure to remove this heat causes the element to burn open. See illustration.
Electric jacket water heaters that have failed.
There are three main causes for premature failures of these elements:
...All air is not bled from the system after a replacement.
...Cooling passages are blocked preventing proper coolant flow away from the element. Steam pockets then develop around the element causing failure.
...Incorrect power voltage is applied to the element. For example: 240 Volts to a 120 Volt element.
When removing a failed element, look for signs of overheating such as:
...A hole melted in the case. See illustration.
...Soot is present on the case and can be wiped off with the finger (or shop towel).
...Also notice if the coolant level shows on the element below the melted case.
...A bad connection at the element-to-cord will show as a melted or discolored connector pin and can also cause the element to burn open.
An open element that has given its expected service life and has none of the above signs was working correctly. When a replacement lasts only a few hours and shows overheating, look for one or more of the previous causes. The element is not at fault.