Here we discuss the main components of the heater circuit and the specific symptoms that may be associated with each.  Testing techniques and possible fixes are listed.

Note! Digital systems with printed circuit boards typically do not use mechanical thermostats and high limits, They use electronic temperature sensing devices.  They may use a contactor and pressure switch, and GFCI tripping issues may still involve the heater. Some tests will be the same.

Thermostat:  (Symptoms: no heat, too hot, not hot enough)
Mechanical thermostats consist of a switch, control knob, and temperature sensor.  The temperature sensor looks like a copper wire when in fact it is a tube connected to a bulb which is filled with freon which expands and contracts with temperature.  It is this expansion and contraction that activates the switch.  If your spa is too hot and does not respond to a turning down of the thermostat, this bulb could be corroded.  Check it.  If so, the gas may have escaped and thus while the switch will activate you'll have no sensing capabilities so it won't turn off at any designated temperature.  Bulbs cannot be replaced.  Time for a new Thermostat.  If your pump does not respond to thermostat demand you may want to check through the thermostat with your meter on ohms and power off to be sure the switch is opening and closing. You can usually hear this if your ears are good.  The switch will make a faint click as it is engaged and disengaged.  If it is engaging your problem may be up or down the line.  A power on check will assure you the T-Stat is getting power.  Meter to AC volts check each side to ground. 

If your spa is not hot enough, you may find that the thermostat is out of adjustment.  If you remove it from the heater (power off of course)  you'll find an allen screw adjustment on the bottom.  a quarter turn clockwise will usually  increase the temperature to comfortable levels... A word of caution here.  

It is UNSAFE to use your spa at temperatures above 104 degrees! It raises your core body temperature and can cause flu like symptoms.  It can also kill you!  Even at 104 degrees you should limit your time in the spa to no more than 15 minutes.  Some people shouldn't use a spa that's hotter than body temperature.  Consult your doctor!!!  Drugs and alcohol do not mix with spas either!  If you turn up your thermostat it's your responsibility to be sure your spa is not too hot for safe use.  Get a good thermometer that will give you an accurate reading.

High Limit: (Symptoms:  no power, no heat, high limit trips too soon)
High limits are also temperature sensing switches. They also use sensing bulbs so the same problems that exist above can influence your high limit.  If your high limit is tripping within a few minutes of activating the heater CHECK FLOW! Little or no water flow will cause this. 

If it trips at the end of the heating cycle it's probably because at the end, when the thermostat turns the pump off,  the element is still hot, and the water is hot.  The temperature at the element  can go up for a few seconds and will sometimes trip the high limit.  It's best to replace the high limit if this happens all the time. The high limit has an adjustment screw also.  If you choose to try this it is a counter clockwise turn and it should barely be tweaked.  You need this safety switch to interrupt if there is a problem. 

This adjustment is at your own risk!  Remember flow is critical!  If you adjust your high limit and your pump impeller is full of leaves you could have a complete meltdown of all pipes in contact with the heater.  Not a pretty sight!  If you have no power this can also indicate a "high limit tripped" condition.

Pressure Switch: (Symptoms: contactor not closing, no heat.)
Obviously, flow is going to come up again here!  You must have flow for the pressure switch to activate!  To check for activation:  with power off, disconnect the leads going to the pressure switch.  Make sure they aren't touching anything.  Power up and turn on low pump. With your meter on ohms, check across the poles of the switch. You should have continuity. If not and you know flow is not the issue, most pressure switches have an adjusting collar that will vary the pressure it takes to activate it.  Counter clockwise turns decrease pressure required.  Turn the power off  before attempting any adjustment!  Make all adjustments slowly and try again. WARNING, if you go too far the pressure switch may activate with the pump off. 

This is the last thing you want to happen!!!  Always check to be sure that the heater goes off when the pump does!   If you are certain flow is present, but your pressure switch isn't activating you may want to remove it and be sure no debris is clogging it up.  Pressure switches are in contact with the water, when you remove it water will come out (or should).  Power off!  Close valves. 

Sometimes the location of the pressure switch is such that removal is impossible without removing other components (I hate that!) Some use a plastic base and must be unscrewed very carefully or the darn thing will break off. Now you'll have to dig out the old threads and replace your switch.

Flow Switch: (Symptoms:  GFI trips, no heat)
I haven't said too much about these as they aren't as common as pressure switches.  They are usually in the plumbing close to the heart of the action.  They are gray or white with a small cord coming out of them that goes to the controller. They utilize a little paddle type device that is pushed by water flow until it activates a little switch.  The switch should be isolated from the water. 

If, when you open your flow switch water comes out, you must replace it.  Otherwise, with the power off remove the leads to the terminals, make sure they aren't touching anything and power up.  With flow established check the switch to be sure it is closing using your meter set on ohms.  You should have continuity through the switch.  If not, time to replace. The wires, though small, carry 120 volts.  Don't leave them hanging.

Contactors: (Symptoms:  no heat, buzzing, GFI trips)
Contactors close when the control loop is complete. They consist of a coil which when energized should pull down the contacts so the voltage to the element can pass through.  Troubleshooting a contactor consists of checking across the coil (not the contacts) to see if the circuit to it has been completed.  Coils can be 120 volt or 240 volt with 120 being the most common.   This is a power on test so be careful.  With your meter set to AC volts activate all controls necessary to activate your heater. Turn up the thermostat to engage your low pump. 

Check across the coil of the contactor for voltage (neutral and hot side for 120 volts).  If you find the proper amount of voltage present and your contactor is not engaging it is bad.  If you do NOT have voltage at the coil there is an open switch somewhere in the control loop, you'll need to go back through your switches.  If your contactor is buzzing replace it. There may be more than one contactor.  Make sure you are checking the heater contactor by tracing back the wires from your element.

The Element: (Symptoms:  GFI trips, no heat)
Before we start it is important to note that if the spa is heating AT ALL it is not the element. See thermostat.  Assuming this is not the case continue with the power off, disconnect all leads connected directly to the element.  With your meter on ohms test across the element terminals for continuity.  If there is no continuity your element is bad.  If  you have continuity it should be around 9 to 12 ohms.  If your GFI is tripping, check from ground to each element terminal.  The slightest flicker of continuity indicates a fault to ground and your element is bad even it it has continuity between the terminals. It may have a pinhole in it or be otherwise corroded and leaking current to ground. This is a potentially lethal situation and your GFI is doing it's job. Do not bypass GFI (ever!), even if your element looks okay! 

Spa Switches and Relays

Common Spa Switches

Inside a spa control,  electricity follows a path provided by wires and switches. A switch is simply a device that provides a bridge for electricity to cross (or not) between two contact points or poles.  When the switch is closed it allows the electricity to follow the path through it.  When "open"  there isn’t a bridge, therefore, no path. Digital spa controls utilize switches and relays mounted on a printed circuit board and these can be difficult if not impossible to troubleshoot.  Mechanical spa controls have physical swithces and relays attatched by visible wiring that can be traced.  Much of the efforts here, will concern this type switch.  The wiring logic however is similar, so even if you are troubleshooting a digital control you can use the information here to try and eliminate possible problems. A simple "single pole" switch when closed (on) allows power to go through and light a light bulb for example.  When open (off) there isn’t a path and no light.  These switches are also known as single pole single throw switches, one way in for electricity one way out. There are many single pole switches to be found in any spa system.  Testing them, to be sure they are working requires being able to activate the various switch activation mechanisms found and testing for continuity through the contact points, i.e. where the wires connect.  Removal of the wires from these "contact" poles is necessary so that you aren’t getting feedback from up or downstream.  These are power off tests with your multimeter set on ohms.  Since knowing how to activate the switch is part of the battle, we’ll go through all the single pole switches found in spa systems.

Thermostats (electromechanical) can be activated by turning them up with the power off.  If you listen carefully you will hear a faint click as you turn the temperature knob up.  That is the sound of the switch closing.  You’ll also hear it as you turn it down.  If you remove the wires from each side of the T-stat and place your meter probes across the poles you should have continuity (almost zero resistance) when you close the switch.  When you turn it down you shouldn’t have continuity after the switch "breaks."

High limit switches have a reset button that pops out when tripped.  This opens the switch allowing no path.  If the button is not popped out you should  have continuity through the poles of the high limit. this can be tested with the power off with your ohm meter.

Pressure Switches exist to prove water flow before activating the heater relay. They operate by water pressure to a bellows that pushes up a rod  pressing on the switch activator. To test without power, they must be manually activated which can be a little tricky because the activating button is underneath the micro switch.  You have to stick a little flathead screwdriver in there to activate the switch because with power off you won’t have  pressure.  Be sure to remove the wires from it to test.  

Time clocks have switches too.  If you are troubleshooting a time clock on a portable spa control, first determine which wires are the time clock motor wires.  These are not the poles you want to check.  You want the time clock switch wires.  If you look you’ll see a diagram that shows the switch symbol something like this:  –/ — Those are the poles to remove the wires from and check.  Activate the switch by turning the timeclock knob clockwise until it clicks. Note: An important fact that may help is that usually only hot legs are switched.  You’ll notice that most neutrals (whites) are tied together and only serve to "complete the circuit."  Neutrals will be found on coils of contactors and relays but are rarely "switched."  That will become more clear to you as you delve into your system. Now that you’ve learned about single pole single throw switches it’s time to move on to another common switch type found in spa systems.

Single pole double throw switch. 

The spdt switch allows for two separate paths for the electricity to follow.  Power enters this switch via a "common" pole.  When the switch is not active the bridge to the "normally closed" or NC pole is closed.  When the switch activator is engaged the bridge to the "normally open" or NO pole is closed.  It is the spdt switch that provides the basis for the relay logic necessary to run spa systems.  Air activated relays often use spdt switches. For instance, almost all portable spas utilize a two speed pump motor.  This motor can run on high speed or low speed but not both.  Feeding power to both the low speed and high speed windings at the same time causes a frightful noise with an overload lock out in less than a minute.  This is prevented by the use of single pole double throw switches.  The common pole of the switch carries the power that will be used to run both high and low.  With the switch at "rest" the low speed runs.  When the switch is activated the high speed runs but never both together.  Cool, huh? Now, consider the fact that in a 120 volt spa you have a heater that can only run with the low speed pump.  The heater can’t run with the blower, only because there is no pump running and it will burn up.  High pump and heater can’t run together, there isn’t enough current at 120 volts/20 amp circuit.  Obviously there would be an overload with high pump and blower together.  Now you get a sense of why there are banks of relays to handle this logic. The Common Micro switch is found on many different relays in an electromechanical system.  Your Pressure switch is likely to have one.  Flow switches use them, relay banks use them. Air receiving relays have them as well. Sometimes, even thought the the switch may be a spdt switch only one "throw" pole is used.

Spa Relays

Now that you’re feeling more comfortable with switches lets move on to relays.  A relay is a switch with an activating mechanism attached, Some relays get a little more complicated in that they usually serve as a mount for several switches and can be powered by air (air receiving relays) or a magnetic coil like a contactor

Air receiving relays receive the air that is passed through the tube connected to your button  at spa side.  They are of two types: latching and non-latching (or momentary). They look identical.  Latching air receiving relays may actually run the equipment.  They will directly feed pumps, blowers, lights and even heaters. They can come with one, two or three micro switches. A single pole will have only one microswitch, a double pole will have 2, etc. There are four function "cam" action air receiving relays that can run every piece of equipment in a 120 volt portable spa.  Pump, pump and blower… blower only…. and low speed/heat with T-stat demand.  When you  press your button on the spa the force of the air moves an arm that comes up and turns a cam that activates the micro switches in sequence. Momentary air receiving relays generally send a pulse of electricity to the coil of a coil activated relay.  This causes a rod or plunger to move and in various ways activate a switch or switches on the relay.  When you push your button again – it again sends a pulse which will cause the relay to move to another position or move back to the original position. A word about coil voltages, while 240 volt coils and 12 volt coils are not unheard of most likely your coil voltage will be 120 volts.  Be sure of it though. It should say on the coil what the rating is.  It will also say what the switch rating is, study it to be sure you know which is which.  On Potter Brumfield coils the number at the top is the coil rating.

Contactors are a heavy duty relay that allow for heavier current flow, like to a heater.  Supply wires to a heater are large wires.  Contactors have the capacity to handle the wire size and the current flow and are activated by coils.  This allows for smaller wires to be used through the "control loop:" T-stat, high limit, pressure switch to the coil of the contactor. Many spa systems utilize cube relays which are type of coil activated relay that does not use a micro switch.  They are sometimes a little difficult to troubleshoot because you often can’t see what they are doing.  The coil poles are at the very bottom.  Common poles in the middle and normally open on top of that.  Often, the normally closed poles are snipped off, but sometimes present they are located at the top. USUALLY, but not always left and right is electrically isolated.  

Basic troubleshooting of spa switches and relays requires understanding the above and knowing how your spa works.  If your complaint is no heat, for instance, and you have established that you have flow and know your high limit isn’t tripped you must isolate the circuit and backtrack through it.  Knowing that your heater and low pump will work together helps.  If turning up your T-stat activates your low pump but not your heater contactor then start at the coil of the contactor.  With the power on, and a call for heat, (thermostat up) Set your  meter on volts:  Measure voltage across the coil of the contactor. This is the activating part of the contactor. If you have 120 volts there then your contactor should be activating.  If it’s not, it’s bad.  If you measure no voltage at the contactor then your problem is upstream of it.  Look for where it stops.  Do you have power to the T-stat? Out of it? To the high limit?  Out of it? To the pressure switch? Out of it?  Just trace the path.  If you have power in, but not out, that will be your problem component.

Obviously power on tests require great care for your personal safety and some measure of experience with an electrical meter.  Don’t attempt these tests if you are beyond your comfort level. Call a qualified technician.

The big thing to remember when you open up your box and the words "Oh God" come unbidden to your lips, you will be tracing individual problem circuits.  Sometimes, I do sit for awhile and contemplate the why did they do it like that concept, but if I’ve got a heater not working I’m only working with the spa heater circuit and maybe the low pump circuit.  You can easily isolate each component by following its power cord into the box.  Two speed pumps have 4 wires: red, black, white and green.  Red is usually low.  Blowers have 3 wires.  Lights have 2.  Heaters may have two or more see heater help for clarification.  Spa side controls with thermostats and air buttons have 6 wires. The ones you are concerned about are the red and the black.  Black is power to the thermostat, red returns it to the contactor or heater relay perhaps via the high limit and pressure switch.  Just FYI, the other wires of the 6 are white which is neutral, green is ground, yellow indicator light is for jets, orange indicator light is for blower. NOTE on the newer spasides that have an led temperature display the orange is used to power the display and the thermostat. The orange wire for these spa sides must be attatched to a terminal that is hot all the time and LINE 1 Only!

There are some manufacturers out there that really do like to confuse us.  Systems that have a lot of cube relays jumping from one to another can be difficult to troubleshoot, even for me!  This relay activates another relay and you can’t visibly see the action of the darn thing.  That’s why  with older controllers with multiple problems you may want to consider a new control system.  We have many starting at under 300 dollars. They also include heaters too so if you need to cut your losses and start fresh, we can help!  if you have one of those cube relay nightmares or if your spa control has seen better days check out the  spa control selection we have at spapartsnet.com    If you have questions on troubleshooting your relays just call us… tech support is always free and we are glad to help!   813 235 4574   All Techs will be able to help you!