How-To Guides | Heater Element Testing

Caution: Electrical repairs can be dangerous, especially around water. Repairs must be made by a qualified electrician or spa technician. Regardless of who performs the work, disconnect all electrical power to the hot tub prior to any inspection or repair.

Shut power off at the service panel, and as a secondary precaution, disconnect the power to the spa as well. Do not attempt to perform electrical repairs unless you are qualified.


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

Spa heaters consist of an element inside a stainless steel housing. As water flows through the housing, heat is exchanged from the element to the water.

The assembly may also incorporate sensors: hot tub high limit switch and thermostat. Heater assemblies come in various forms.

Common Symptoms & Causes of Heater Failure:

No heat

A heating element is similar to a light bulb in that the filament is a heating coil. In time these can break or burn out. Assuming the control system and pumps are working properly, no heat can indicate a burned-out or broken heating coil.

Note: Catastrophic failure of the heater element can be caused by a dry fire. This occurs when the heater is operated with little to no water present, or with greatly reduced water flow.

The result can be a melted heating coil and/or outer sheath. The element will often have visible signs of damage when a dry fire occurs. Although properly functioning safety devices are designed to help prevent dry-fire, like all devices, these too can fail in spas.

Reduced heat

Low heat is more often caused by a reduced water flow rather than an electrical problem with the heater itself. Check your filter to make sure it's not clogged, and that there aren't other obstructions restricting spa water flow. Excessive scale buildup on the heater element, as a result of poor water balance, can reduce heating efficiency.

Preventing Scale Buildup

Calcium buildup not only reduces heater efficiency, it eventually results in element failure. Regular use of Spa System Flush can help eliminate scale.

GFCI tripping

A heater causing the GFCI to trip, usually indicates a short caused by water intrusion into the element's outer sheath. Water can seep inside at various other entry points like the epoxy seal or the braze. The most common cause will be a pin hole in the sheath caused by corrosion.

When electrical current finds a path from the heating coil to the water, the short will trip the GFCI. If you do see a hole in the sheath, there's no need to proceed with testing- the element is toast!

Testing the Heater Element

Evaluate heater elements by first disconnecting both power leads from the heater terminals, then taking measurements with an ohm meter.

Disconnect all electrical power to the spa prior to any inspection or repair, and before heater removal and testing.

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 element terminals. The acceptable resistance range for most heaters is between 9-12Ω (ohms), some may be as high as 20Ω.

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.

Testing for Shorts

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.

Installing a Replacement Spa Heater Element

When connecting the electrical wires to a heater element, always use two wrenches to avoid terminal damage. Hold your lower wrench stationary while firmly tightening the top nut. This will prevent twisting of the terminal pin, or fracturing its epoxy potting.

Testing Associated Heater Components

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 the wires to each and checking for continuity through the switch. Keep in mind that high limits and thermostats are merely on/off switches which are triggered by heat sensors. 

High Limit Switch

These are normally closed (continuity) but trip open with excessive temperature, which protects the heater element.  Check between the two terminals.  If there is no continuity, the high limit has tripped. Depress reset button & retest.


Functioning thermostats are closed when turned fully clockwise, and open when turned fully counter-clockwise. A multi-meter should show continuity when clockwise, and an open circuit (no continuity) when counter-clockwise.

An Ounce of Prevention

You can protect your spa heater, and prolong its life by observing a few simple rules:

  • Important: Be careful when installing new heater elements. Never bend, push, or twist the electrical terminal. This could cause a fracture of the epoxy seal and lead to water intrusion. Always use two wrenches to tighten or loosen the terminal nut. Hold one wrench on the terminal hex to keep it from turning. Use the other wrench to tighten or loosen the terminal nut.
  • Avoid air locks. After servicing equipment or when filling a dry spa, make sure all air is purged from the plumbing. Dead air in the heater assembly tube can cause rapid overheating of the element, called a dry fire. After refilling the spa, but before connecting the power, loosen a union enough to evacuate trapped air (you'll hear it). Hand tighten when all the air has been purged. Make sure your plumbing system is free of leaks.
  • Keep your hot tub's water balanced. This prevents corrosion of heater parts by acidic water (pH to low) and prevents heater scale buildup from high pH. A few cents worth of balancing chemicals can save an expensive repair, and the trouble of replacing.
  • Maintain sanitizer in hot tubs. Slimy brown film inside a spa may be evidence of metal dissolving bacteria that is slowly eating the heater sheath. This will not be a problem if spa shock is periodically applied and sanitizer maintained.
  • Prolong heater life by setting heating cycles by time of day rather than relying upon thermostatic demand. Switching a heater on and off many times per day puts more strain on the element. If your spa does not have a timer, don't lose any sleep over it.
  • A defective control, such as a chattering contactor or thermostat, can pulse power rapidly on and off, causing premature failure. If a replacement heater burns out quickly, this is something to look for.

Read Caution Statement

Replacement Heater Elements

"I found my replacement flow through element in your heater element section.  Your titanium heater was less than the competition wanted for an incoloy element, so I got a spare too. Thanks also for the fast delivery. It fit perfect and replacing it was easy."

Reginald Estes
Bedford, VA

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