repairs can be dangerous, especially around water. Repairs
must be made by a qualified
electrician or spa technician. Regardless of who performs
the work, make certain that all electrical power to the hot
tub or spa is disconnected prior to making any inspections
Shut the 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
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
Common Symptoms & Causes of Heater Failure:
A heating element is similar to a light bulb in
that its filament  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 thermostat and
limit switches 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 heating coil  and/or
sheath  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.
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 is not clogged, and
that there are no other obstructions restricting spa water flow.
Excessive scale buildup on the heater element, as a result of poor water
balance, can reduce heating efficiency. See
Preventing Scale Buildup
Left is an example of a spa heater element suffering from calcium scale buildup. This buildup not only reduces heater efficiency, it eventually results in element failure. Regular use of Spa System Flush can help eliminate scale.
A heater causing the GFCI to trip, even
intermittently, more often
than not 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 element is toast!
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.
Photo credit: Kaisa Williams
|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 as shown. 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
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 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
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. The
photos below show the ohm meter test points for each component.
|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.
Meter should indicate a continuity when clockwise, and an open
circuit (no continuity) when counter-clockwise.
If your hot tub's heater element, thermostat, and
high limit switch all check out good, refer to our
Tub Equipment Troubleshooting Guide.
Note: Flow and pressure switches are not
pictured, but perform the same protective function by interrupting
power to the heater when sufficient water is not flowing. Either
of these can wear out, and flow switches can be prone to malfunction
due to debris interference.
An Ounce of Prevention
You can protect your spa heater, and prolong its
life by observing a few simple rules:
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, and one on the
terminal nut  for tightening or loosening.
- 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 let trapped air escape (you'll hear it). Hand
tighten when all the air has been purged. Make sure your plumbing system is free of
- Keep your hot tub's
balanced. This will prevent corrosion of heater parts by
water which is too acidic (pH to low) and prevent heater scale
buildup caused by pH too high. A few cents worth of balancing
chemicals can save an expensive repair, and the trouble of
in hot tubs. A slimy brown film on the inside wall of a spa
may be evidence of a metal dissolving bacteria that is slowly
gnawing away at the heater sheath. This will not be a problem
shock is periodically applied and sanitizer maintained.
- If your spa's control system allows for
setting heating cycles by time of day, rather than thermostatic
demand of heat cycles, this will prolong heater life.
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 and
cause premature failure. If a replacement heater burns out quickly,
this is something to look for.