First let me say I have no idea as to the manufacturer of the spa. I inherited it from the previous owner.

It worked fine for a good while, maintained a temp of 104. Cover is brand new and works great.

Last weekend I added some water because the level was low. No leak but just didn't fill it high enough the first time. I did not change the thermostat setting (it's an old dial with tick marks). I came out the next day and the heater was on, and the temp on the termometer was 110 !. I'm not sure why the heater was on; it should have gone off at 104.

So then the heater wouldn't click on at all. I looked for the high limit switch but could not find out how to reset it, so I figured it was probably internal and when the temp cooled down it would reset itself.

Sure enough, when the temp dropped the heater was able to click on. Great I thought...back to normal.

Well, I went out last night (week later) to find the heater on, with the same setting as what should be 104...and now the thermometer reads 94. I'm getting flow, but I don't know where to go from here...

Thanks for the advice. I'm handy with a multimeter and know how to work with (and respect) electricity, so I'm confident I can solve the problem...just don't know where to start.

Hi mchad21,
Your thermostat may have failed, but we need more information on the unit (pictures etc. ) before we can point you in the right direction.

ok thanks for the quick reply !! I'll get some photos in the morning. What exactly would I need to take a photo of? And what exactly comprises the thermostat? I see the thermocouple/sensor in the water, but not sure what exactly has 'failed'.

THe unit's faceplate says 'TDI Command Center'. It's a dial type thermostat with no digital readout, if that helps.

Thanks again !

Hi mchad21,
Controller, and controls (spaside), Brand name of equipment, and or spa,
wiring configuration 110v- 220v and year if possible.

These guys are pretty good, and sometimes just the brand and year of controls will suffice.

The year I have no idea, the spa side controls I can get the faceplate info tomorrow.

It's 120V.

When you say wiring configuration, what info are you looking for?

I did a little surfing and it looks like I can remove the controller faceplate and replace the thermostat..?

I'm sure it will be very easy once I understand it better. Tomorrow I"ll be able to see it in the light of day and get a better handle on how things are connected.

Looking forward to it !!

So you don't suspect the heating element? Why or why not?

Also, I have noticed that the thermostat did not hold a tight temperature; i.e. I would have to turn the dial quite a bit to get the heater to click on or off. I don't know if thermostats fail completely or degrade over time, but if it's the latter I definately had been noticing that the temp control was not what is used to be.

Hi mchad21,

The TDI Command center is a generic ( and good ) Spa side controller.

http://spapartsnet.com/Reference-Catalo ... 3_0_1.html


Tri Delta Industries has been producing spa side controllers (thermostats) for a long time. If your TDI has a grey cable going to a plastic bulb (thermistor) in a dry well (Plastic tube ), then it is a solid state controller. I don't see a lot of those overheating a spa, so the problem may lie elsewhere.

The box that the TDI plugs into is what we need info on. It should say somewhere on it the manufacturer.

Let us know when ya have a chance

Thanks. Mine sort of looks like that..I"m sure I have an older model. I know that there is some info on the 'box' that the controller plugs into. I"ll get it first thing tomorrow.

What other culprits may have caused this problem? I don't know exactly how the system works, but if the thermostat was bad, wouldn't it not call for heat, or call for heat constantly? The latter happened and the temp went up to 110, and the heater did not shut off. But now the heater is on continuously, and from what I can see, there is no heat. So if the thermostat was bad, you should either have a) no heater activiation, or b) heater on all the time.

If the latter occurs, then the temp should now be at 110.

Maybe it's not the problem?

Hi mchad21,

A typical overheat is the result of a runaway thermostat. Mechanical Thermostats with microswitches, and toungston (sp) points tend to have a propensity to stick with age. As the switch paddle moves from the "Ready"points to the "Heat" points, arcing and pitting of the contacts occour. all it takes is one episode of a physicly stuck set of points, and we are too hot to get into. This is where the "high limit switch" comes to save the day. It's design is the same as the t-stat, however it's callibration is 122-126 degrees in the heater chamber.
A solid state controller doesn't suffer the same wear, and usually fails differently.
Another remote possibility is a mild short from the element on line 2 to casing ground, completing a circuit of a piloted leg, causing a glowing of the element. ( What?)
That's why I want to know of the box.
Either way it's broke

wow, looks like I'm going to learn a lot from you..!

I see how it could fail and overheat, but why then would it not overheat again? Apparently it's calling for heat, and has been for a while continuously, but the temp is not even close to what it was before (110degrees).

Something I just can wrap my brain around.

Hi mchad21,

I'll bet your high limit switch did trip.
High limits are required by UL, and without them, you would have a unique work of modern art in your backyard.
As the switch tripped, it killed one phase of your heater, and now the system is desperately running, and running to heat in accordance to the t-stat.
Some manufacturers tie in the high limit to the pumps, and heater, and others to the entire system via a "Systems Contatctor". If yours just kills the heater, then the rest of the system is oblivious to the problem.

I have seen ( or felt ) high limit reset buttons located in a position requiring a mastering of "Twister" to reset.

( Keep in mind I havent seen this unit, and may be way off base)