Hot Tub Spa -
Heater Troubleshooting Guide
The term "Mechanical Failure"
covers everything from shipping damage to dog bite, but the most common mechanical
failures in electric heaters are caused by improper handling - destroying the Epoxy End
Seal, and breaking or twisting the Cold Pin until it breaks are the two leaders in this
failure mode. Because they are so closely related well look at them together .
Any form of rough handling can put pressure
on the part of the heater that sticks out the most - the Electrical Terminal, which is
welded to the Cold Pin, which in turn passes through the Epoxy End Seal to get to the
Heating Coil inside of the element. If the Electrical Terminal is broken away from the
Cold Pin there is obviously no way to connect electrical wires to the heater, and it
becomes a throw away.
More often the rough handling results in the
destruction of the Epoxy End Seal. This will allow moisture to get into the inside of the
element where it will be absorbed by the MGO Filler element and will eventually cause an
electrical short circuit between either the electrically "hot" Cold Pin or
Heating Coil, and and the electrically grounded Outer Sheath of the heater. With luck,
there will be a GFCI on the system that will open the circuit.
If you dont know what caused the GFCI
to turn the power off, you might start investigating "nuisance tripping".
Without the GFCI there will eventually be
arcs, sparks, flames and anger - you can bet on that.
HOW CAN THIS BE PREVENTED?
Moisture may get inside of the element when
it is off. Part of the cooling off process is to suck in any surrounding air through any
crack. Then, the next time the element is energized, the moisture in the element may
provide a path for current to flow, and the GFCI will trip. But, a BIG BUT, - the heater
may have been on just long enough to produce enough heat to drive that moisture out of
there. You come along and reset the GFCI - and the heater will come back on again. Drive
ya nutty, as they say. Check that Epoxy End Seal carefully.
Never bend, push, or twist the electrical
terminal. Always use two wrenches to tighten or loosen the Terminal Nut. One wrench
holding the Terminal Hex to keep it from turning, and one on the Terminal Nut to do the
tightening or loosening.
The trick to analyzing this failure is to
carefully examine the Epoxy End Seal. Signs of severe fracture or chipping are an almost
sure bet that the End Seal is no longer able to do its job - to seal. If the heater has
been acting strangely - erratic- sometimes working fine and other times tripping the GFCI:
look at that Epoxy End Seal.
THE NOISY HEATERS - HUMS, VIBRATIONS,
SQUEALS, TWITTERS, SQUEALS, TWITTERS, SHRIEKS, SCREAMS, RATTLES, WHISTLES, TWEETS, &
Rarely, maybe never, is the element itself at
fault when noise is reported in a heater, even though it is the element that is usually
making the noise. The huge amount of water moving rapidly past the element can set up some
wild vibration patterns as it twists and turns through the heater. Usually it is simply a
matter of re-aligning the element by a bit of gentle bending to move it away from the
heater housing; or tying the noisy part down with a clip or wire made for the purpose.
Check with us.
DRY FIRE- THE ULTIMATE ELEMENT DESTROYER
SETTING THE STAGE
In the normal operation the heaters that we
deal with daily in pools and spas operate at temperatures only a few degrees above the
temperature of the water that is flowing past them. If the thermostat in a spa is set up
to maintain the water at 102º, for example, the temperature of the Incoloy Outer Sheath
will be about 110º. The water flowing past the element is carrying the heat away just
about as fast as the element can produce it. Everyone is happy.
WHAT GOES WRONG?
One of three things can happen - A) the water
flow slows down too much, B) the water flow stops, or C) the heater is somehow turned on
with either no water in the housing, or only partially filled. The results will be the
same: the Incoloy Outer Sheath temperature will rapidly rise - 200º - 500º - 1,000º -
1,500º in a matter of just a minute or two. This is approaching the melting point of the
Sheath and it will get there quickly if it isnt turned off by some safety device
like a high limit switch. The failure can show up in several different ways:
- The Outer Sheath splits open. The Heating
Coil wire is hanging out in all directions and the MGO Filler is cracked, smashed and
blown away. The element is totally destroyed, and frequently the Stainless Steel Heater
Housing may be damaged as well.
- Just one or two small holes are blown through
the Sheath - not as dramatic as a complete, explosive meltdown, but just as costly. The
element is destroyed.
- No holes are visible, but the walls of the
Sheath are bulged outward in spots, the normally smooth surface of the Sheath are now
bumpy and has become discolored. Inside of the element the Heating Coil may be broken; or
it might be electrically shorted against the Sheath. Or both.
WHY? WHY? WHY?
Those are three good questions. Lets
take a look at a few of the things we have learned from a lot of field experience plus a
ton of hours in the engineering lab:
HIGH LIMIT PROTECTION - the primary job of
the High Limit Switch in the finished product is to prevent scalding water from ever
reaching the people using the product. Sure, the thermostat should shut the heater off
long before the point at which the High Limit Switch is needed, but thermostats, like
everything else, fail.
Will the High Limit do its job? It
hasnt had to operate for months or years - is it ready? Is it in the right place to
do the job? If the High Limit is not sensing the water temperature close to the element,
and the pump suddenly quits - its dry fire time in just a minute or two. The element
will boil the water in the heater housing - and create its own "dry condition.
Following that, the service technician
arrives and finds the heater assembly full of water again, and claims that it
couldnt have been a dry fire. Check that high limit.
FLOW / PRESSURE SWITCHES - various types of
devices are used to detect whether there is any water flowing through the heater assembly.
Unfortunately, when these things fail, they generally fail in the closed position and
there is no indication that they are not doing their job. In most cases a spa system will
work just fine with a stuck pressure or low switch - until there is a need for it.
If a full scale dry-fire destroys the
flow or pressure switch along with the element, its impossible to determine which
went first; but one thing is certain - the heater was doing its job. It isnt very
smart - it just makes heat.
ATTACK OF THE KILLER CHEMICALS
CORROSION - THE BAD GUY
Its a mean, angry sounding word,
bringing visions of all sorts of nasty things. Even the dictionary makes it sound pretty
akin to rodent" no less. Come to think of it, weve seen a few
heaters that looked like rats had been gnawing on em.
We think its a safe bet to say that one
of the major causes of heater failure has always been corrosion. Given any chance at all,
this demon will destroy a heater element or, in many cases, the entire heater.
The corrosion that we come across in our
industry, particularly in spa equipment, comes in many varieties, each with its own name
and characteristics - we are faced with galvanic corrosion, chemical pitting,
intergranular corrosion, stress corrosion cracking, corrosion fatigue, we even have a
strain of bacteria: Ferrobacillus in the Siderocapsaceae family, also called
"iron eating bacteria," to contend with. Gee Whiz.
WHAT CAUSES ALL OF THIS?
Well, a full discussion of the chemistry and
electrochemistry involved with this pretty complex subject is beyond the intent of this
Handy - Dandy Guide. Its much easier to describe what doesnt cause it
than to attempt to explain all of the chemistry that does. Consider this: if all of those
spas out there were filled with clean, pure water, and no one ever added any chemicals to
them, the word corrosion would soon leave our vocabulary.
Unfortunately, thats not going to
happen, and all of those spas are going to continue being filled with water of every type,
from the Cascade Mountains rain water to big-city sludge.
A DEADLY SOUP
Then, to add to the problem, we have learned
that many, many spa owners are not following all of the instructions theyve been
given about pH, Total Alkalinity, Calcium Hardness and Total Dissolved Solids; or about
how to handle those unique water problems that may exist in their spa when it is filled
with water from their tap.
LOW pH - BOO! HISS!
If we had to pick the worst offender in the
corrosion list, it would definitely be LOW pH, because as wed all learned long ago: when a
test sample of the water shows a low pH (below 7.0), it indicates that the water is
acidic. Remember now, this is not just saying that there is acid in the water - it says
that the water has become an acid. It doesnt matter at all what kind of acid caused
this to happen - hypochlorous, hydrochloric, hypobromous, muriatic or whatever - when the
water becomes an acid it becomes a starving, hungry, corrosive beast looking for lunch.
Acids will corrode - eat away - almost any metal in their path in order to satisfy that
An element or heater corroded because
the water has a low pH is easy to spot - it has pieces eaten away from its surface. Gone,
disappeared, departed. It looks like the craters of the moon. And people are putting their
bodies in there!
SCALE / CALCIFICATION - HISS! BOO!
At the other end of the ----- we have SCALE.
In some ways scale can be considered as the opposite of acid: with scale the water has too
much of something and wants to get rid of it, and the nice warm heating element is a good
place to deposit it. The problem is that its like asking a Hawaiian to run a
marathon in Honolulu dressed in a fur coat, wool cap and mukluks. Hes going to have
a rough time getting rid of the heat hes generating, and probably wont finish
and then again
Bad-chemistry corrosion can show up where the
element sheath is brazed to the bulkhead fitting, or welded to a mounting plate. Even
though all of the parts are "stainless" steel, and selected just for this
purpose, the ingredients (mostly iron, chromium, nickel and molybdenum) in the steel must
vary - the mix has to be different for parts like the Bulkhead Fitting that needs to be
machined, versus the thin, high temp Incoloy Outer Sheath that must be bent and formed.
Very special welding techniques are used at
these joints to make sure that no impurities are left behind that might corrode. But, if
the water gets bad enough, you may see corrosion at these weld points. It can range
anywhere from a rust-like deposit to cracks and fissures in the metal.
At its worst it can result in
"corrosion fatigue," causing the bulkhead fitting to break away from the outer
sheath. This corrosion is bad stuff.
AND THEN: THERES THE IRON EATER
A slippery, brownish coating on the inside
wall of a spa may not be any form of algae, but can be the effects of an "iron eating
bacteria" that is gnawing away at the heater. This one is easy to correct - the water
simply needs some sanitizer: chlorine, bromine, or ozone. A "shock" treatment
would probably be in order here, a drain and a refill if it wont go away.
WHATS THE BOTTOM LINE ON CORROSION?
Corrosion of the metal in a pool or spa
heater happens when the water becomes corrosive because somebody makes mistakes with its
There are more than 2,000,000 spas in the USA
alone that have never shown any signs of corrosion - some more than twenty years old.
Their owners follow the instructions of the professionals at their local pool/spa store,
and maintain a good sanitizer level along with a non-corrosive pH level, and monitor their
Total Alkalinity, Calcium Hardness and Total Dissolved Solids for a good water balance.
They do not "throw in a little of this or a little of that." Thats like
signing a Pledge of Corrosion.
DO THEY EVER JUST "BURN OUT" ?
Its correct to say that the only
"natural" - as in "died of natural causes" - electrical failure that a
resistance-wire heater ever suffers is when the heating coil breaks, causing an OPEN in
the circuit. This is also the only electrical failure ever covered by a warranty.
Its exactly the same as a light bulb
burning out - it just gets tired of the tremendous trauma it goes through each time the
power is applied. Picture it - it goes from cold to very, very hot in less than 1/10th
of a second - it opens a door to see whos knocking and a thousand billion billion
electrons (thats 21 zeros!) rush in during the first second.
Because of the careful selection of
components in the Heating Coil, this sort of failure is actually quite rare. (Have you
ever seen a light bulb burn out while it was on? Probably never - they always burn out
just as you turn them on. Thats "turn on trauma".) However, it can be
brought on more quickly by switching the heater on and off rapidly - this can happen with
a defective control, such as a chattering contactor or thermostat, for example. Be very
suspicious if a replacement heater burns out quickly. Watch for this.
Another suspect in an OPEN situation is a
reduced water flow that causes the element to operate at a much higher temperature than
normal, but not high enough to cause a dry-fire condition. There may be no signs of the
problem on the outside of the element - it just got tired of working too hard.
EVERYTHING YOU ALWAYS WANTED TO KNOW ABOUT
TESTING OF THE ELECTRIC PART OF ELECTRIC HEATERS
THEYRE SIMPLE - REALLY
Of any piece of equipment you might find on a
spa or tub today, the electric heater is probably the most simple, were not talking
about the controls, now - just the heater itself. What makes it simple is that it is a
straight resistive device. It doesnt have any coils like motors and transformers,
giving them inductive characteristics; and it isnt anything at all like a solid
state, printed circuit board mounted, microprocessor based control system. With heaters,
the electrical is plain-Jane
THE IMPORTANT NUMBERS
You can learn just about all there is to know
about an electric heater by applying a little knowledge and a smidgen of easy math, along
with a decent test meter. Well start with the basic numbers:
These first two numbers are stamped or marked
on the heater.
Rated Voltage: 115, 120, 240, or 230 volts
Rated Wattage: 1500,5500 watts or 5.5 kw
These next two are calculated using the above
Calculated Amperage: 12.5, 22.9, 25, or 48
Calculated Ohms:5.0, 9.6, or 10.5 ohms
The math part is kept simple by using our
Handy Dandy Decoder Ring, as shown. Lets say you want to figure the amps rating of a
heater marked 240 volts & 5500 watts. Use w/v: that would be 5500 divided by 240, and
the answer is 22.9 amps. Simple.
The next three are measured with a meter at
an operating heater:
Measured Voltage: 112, 227, or 238 volts
Measured Amps: 11.5, 21, 24.6, or 44 amps
Measured Ohms: 10.4, 9.6, or 4.9 ohms
USING THE NUMBERS
All that follows applies to all electric
heaters. The task is simple - to determine if the heater is producing heat (watts); and
then make sure that it is safe - these are the facts, maam.
First, measure and compare the voltage at the
heater terminals with the voltage at the panel board, receptacle or other power source.
Dont blame the heater for poor performance if this measured voltage is more than 10%
below the heaters rated voltage. (Do the math (v)^2 / o, to see how quickly the
watts drop as volts drop.)
If the measured voltage was much different
than the rated voltage, youll have to re-figure the calculated amps using v / o.
(You cant use w / v, because youre not sure what the wattage is anymore.)
Then, with power still on, put your clamp-on ammeter around one of the heater wires -
either one, but only one. Youre now reading measured amps, which should match the
calculated amps within 10%.
Turn OFF all power, then DISCONNECT BOTH
WIRES from the heater terminals. Set the meter to the Ohm's scale and take the
following readings at the element terminals:
- Terminal - to - terminal: the measured
Ohms should read within 10% of calculated Ohms.
- From each terminal, one at a time, to the
element sheath or element mounting plate: should read OPEN or INFINITY. ANY OTHER READING
says the element is internally shorted. This is a bad element. Look for signs of dry-fire
Thats it. You now know all there is to
know about the electric stuff in the heater. You can now re-calculate the wattage using
the voltage, amps and ohms numbers you have measured, confident in your knowledge.
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