Spa water heater repair
All electrical resistance heaters work the same way: current is passed through a special element, which creates heat. When the current flow is interrupted or diverted, no heat is created.
Heater Element & Assembly
In hot tubs, the element coil is housed in a heater assembly housing, which exchanges heat produced by the element to the water, as it flows through the tube. The assembly may also incorporate sensors: hot tub high limit switch and thermostat. Heater assemblies come in various forms, a common type shown here.
Spa Heater Element Construction
Diagram shows construction of an electric heater element. Note the electrical connection terminal .
Inside is the heating coil , a filament encased in insulating powder . It is surrounded by a sheath of Incoloy , a heat and corrosion resistant alloy which isolates the electrical coil and insulating filler from contact with water.
Reference this diagram when performing diagnostics below.
Common Symptoms & Causes of Heater Failure:
A heating element is similar to a light bulb in that its  is a heating coil which in time can break or burn out. Assuming that the heater's connection  are in good condition, it is properly energized by your hot tub's control system when it should be, and that the and are functioning properly, no heat can indicate a burned-out or broken heating coil, which results in an open circuit.
Note: Catastrophic failure of the heater element can be caused by a dry fire. This occurs when the heater is operated with little or no water present, or a greatly reduced water flow, which can cause the  and/or  to actually melt. The element will often have visible signs of damage when a dry fire occurs. Although properly functioning high limit switches, pressure/flow switches, and thermostats are designed to help prevent this condition, like all devices, these too can fail in hot tubs.
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