Hot Tub heater not working – Kingston Pools and Hot Tubs – Knapp’s Pools and Hot Tubs

Please ensure all power to the spa is shut off before attempting to do any testing or diagnostics

The element

A heating element is similar to a light bulb in that its filament is a heating coil which over time can burn out or break .  Make sure that your heater’s connection terminals are in good condition, (not showing rusting etc) and that it is properly connected to your hot tubs motherboard and that the heat sensor (thermostat)  and high limit sensor are functioning properly.  If you have absolutely no heat this can indicate a burned-out or broken heating coil, which results in an open circuit.
Catastrophic failure of the heater element can be caused by a dry fire situation.   This occurs when the heater is turned on with little or no water present, or a greatly reduced water flow, which can cause the heating coil] and/or outer sheath to physically 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.

Little or reduced heat:

Low heat is more often caused by a reduced water flow rather than an electrical problem with the heater.  Check your filter to make sure it is not clogged, and that there are no obstructions that could be restricting the flow of water.  Also excessive scale build-up on the heater element can reduce heating efficiency.  TCalcium Scale Builduphis occurs when there is improper water balancing by the spa owner.




A heater causing the GFCI to trip, even periodically  indicates a short circuit caused by water intrusion into the heater element’s outer sheath.   Water can seep inside at various other entry points such as the epoxy seal or at the braze, but the most common cause will be a pin hole in the sheath caused by corrosion.  When the electrical current finds a path from the heating coil to the water, the short will cause the GFCI to trip.  If you do see a hole in the sheath, there is no need to proceed with testing.  The heater requires replacement.

Testing the Heater Element

The best and safest way to evaluate heater elements is to first take them out of circuit by disconnecting BOTH power leads from the heater terminals and then take measurements with an ohm meter.  Be certain that all power is disconnected to the spa before making inspections, and before removal and testing of the heater.

Acceptable Resistance Range

To test hot tub heating elements for integrity, use an ohm meter on its lowest setting.  With the meter’s test leads, measure the resistance between the two terminals.  The acceptable resistance range for heaters used in most hot tubs is between 9 – 12 ohms (a few may be as high as 25 ohms, depending upon kilowatt rating).

A reading which is too low indicates a bad unit: short circuit.  A very high (or infinite) reading indicates a bad unit: open circuit or limited conductivity.

Now test for a short to ground.  On the meter’s highest ohm range setting, measure between one element terminal  and the sheath of the element.  You should get an infinite reading on the ohm meter, indicating no continuity to ground.  Any ohms reading indicates a short, and bad element.

If the heater element checks out OK, the problem may be with the high limit switch or the thermostat.  These can be tested by disconnecting both wires to each and checking for continuity.  Keep in mind that high limits and thermostats are merely on/off switches which are triggered by heat sensors.

Please do not attempt to work on your hot tub if you are not an experienced technician.



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