How Does a Hot Tub With a Hi-Limit Switch Work?

The High-Limit Switch

• The high-limit switch is a sensor that signals the water heater to stop operating if temperatures rise too high. Typically, the switch is set to shut off at 120 degrees Fahrenheit. Higher temperatures can damage the heater assembly. To function properly, the high-limit switch requires the free flow of water into the tub and proper calibration of the thermostat, among other factors.

High-Limit Switch Location

• The high-limit switch of a hot tub is included in the water heating assembly. Typically, such an assembly is composed of an insulated heating coil covered by a sheath of corrosion-resistant material. The unit's thermostat is also included in the assembly. The assembly housing is composed of a durable material, such as stainless steel.

How the Hot Tub Operates

• Hot tub water is drawn from the surface by a pump. The pump propels water over the heater assembly. The heat from the coils in the assembly is transferred to the water. Once the water is heated, it flows into tubes and into the tub via jets. The water that reaches the tub is hot enough to soothe away aches and pains. If the tub water is cold, your heating coil may be burned out and in need of replacing. Alternatively, cold or cool water may indicate that your high-limit switch is being falsely triggered.

High-Limit Switch Triggers

• As with sensor elements in many appliances, the high-limit switch can malfunction or trip for reasons other than excessive temperature. If the hot tub filters are clogged or dirty, the flow of water will be restricted. This can cause the high-limit switch to trigger shut-off at temperatures lower than the preset limit. In addition, if you mistakenly turn on the hot tub controls while the tub is dry, temperatures within the heater assembly can rise so high as to melt the assembly itself. High-limit switch issues may occur when you empty your tub and then refill it, as air can fill the pipes that convey water to the tub. The presence of air in the tubes can also cause the high-limit switch to trip. Calibrating the thermostat at too high a temperature is another way to trigger the high-limit switch.