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Heater elements are small, strong wires (filaments) encased in
an insulating powder surrounded by an Incoloy sheath. The
electrical connections are made at the terminals connected to
cold pins attached to the filament. The filament super heats when
power is applied which heats the powder and the sheath.
Portable spa elements are made to be totally immersed in
flowing water to prevent damage from over-heating.
To test the integrity of a heater element, use an Ohm meter on
its lowest setting and measure the resistance between the
terminals. The acceptable range for most portable spa elements
is 9 - 12 Ohms. However depending on the Kilowatt range of the
element a reading of <25 ohms is nothing to worry about. Next
test for a short to ground. On your highest Ohm setting measure
between one element lead and the bulkhead, nut, or sheath of
the element. You should get an infinite reading on your meter
indicating no continuity to ground.
Heater elements are similar to light bulbs in that the filament
cannot "sort of" go bad, it either has connection or it doesn't. The
difference is that an element can be capable of heating and still
need replacing due to allowing current to leak into the water
(short to ground). The causes for a short to ground include: pin
hole failure from chemical damage, overheating due to dry fire,
and overheating due to insufficient water flow.
Testing Heater Components
Heater Element Evaluation
Electric heaters, whether integral or stand alone, have most of the same basic components. One of the ways to
test these components is to disconnect power and check for continuity or resistance across each unit.
Remembering that since Hi-limits, Thermostats, and Pressure Switches are nothing more than a switch activated
other than manually, we will be looking for a short across the terminals. The Element is considered a load, and
will have resistance (usually 9-12 ohms in the case of 1- 6kw elements). None of the components or loads in a
heater circuit should ever show any continuity (or resistance) to ground.
The diagram below illustrates the test points for each component:
To test the thermostat, check
between both leads with knob
turned fully clock wise and fully
counter-clockwise.The meter
should show a short when CW
and an open when CCW.
Test between the two heater leads.
Reading should be 9-12 ohms.
Test here for high limit
contacts. High limits
should read a short
normally. An open
indicates the high limit
has tripped.
The box, element sheath,
thermowell, and element
nut or flange are all
considered ground.
There should never be
any resistance reading at
all between these and any
of the other test points
Magnesium Oxide
powder as insulator
Incoloy Sheath
Tungsten
coil filament
Nut or
Bulkhead
Terminals
Cold Pin
Technical Services
