I noticed one night that the power light was flashing after not having used it for a few days and I checked the water temp and it was down (from 100) to 85. I went to the breaker and it wasnt tripped. So I flipped it off, waited 30 secs, and then back on. Hot tub powered up, and started working but then I noticed the light flashing again the next day and it had no power again.

Called a dealer, they told me it was just a clogged filter so I pulled all 5 and installed previously cleaned filters. Then I reset it with the breaker again and it ran for about 20 mins before shutting down yet again. I tried removing the grey filter and tube that the circ pump uses and it still shut down so it can't be a clogged filter, old or new. While it was running, it did produce heat-- i could see the plume of heated water coming up from the drain in the footwell. I checked the SilentFlow circ pump and its definitely running and not too hot to the touch. It's not in Summer mode. If I reset it and run the jet pump(s) it stays on and works (seemingly) fine. With no jets on it shuts down sooner, but i can't leave it running 24/7.

It needed to be cleaned anyway (4 months) so I poured in a Spa Rinse and ran it for 30 mins per the directions, drained it, cleaned it and refilled it. Yes, I flipped the breaker off before draining. Once refilled I balanced the water the best I could and powered it up and it got from 58 degrees (well water) to about 88 deg in a few hours... so I went to bed. This morning the power led was flashing again and the temp was about 95. So I'm thinking that the heater is doing it's job and something else is causing the shutdowns.

From my auto experience I came up with possible reasons- a bad hi-limit temp switch, bad temp sender, and/or low flow. Any others I didn't think of?

So could this be a bad hi-limit or control thermistor (I bought both just in case) or is the circ pump just not moving the water fast enough? Kinda sounds like the water is boiling in there sometimes; never noticed that before- but I dont have the service panel off most of the time either. I am going to power down, clamp the lines and remove the circ pump to check for binding and corrosion- while it's out I'd like to test it. I have an ohmmeter, but am not exactly sure how to test it. Specs are on the label, so I'm halfway there...

Any tips on replacing the thermistors? I thought I saw Ohm specs for them in another post, but am getting dizzy wading thru all the posts... I'd like to check them too so I can prove to my wife that we don't have to pay the dealer $150 just to show up. Yeah, a service call is $150, not including parts and they won't guarantee that they'll fix it. And if they gotta come back... you guessed it- another $150. Glad I asked.

One more thing- once filled and the jets on I have a nasty ring around the tub and its dark and kinda oily. Is this just residuals that can never really be flushed?
Test results: (well water at 100 deg, 500 gallon tub, bromine sanitizer)
Free Chlorine 3.0
Total Chlorine 3.0
Combined Chlorine 0
pH 8.2
Hardness 40 ppm
Alkalinity 220 ppm
Copper.63 ppm
Iron 1.45 ppm
(TDS and Cyanuric not run)

Thanks for a great site- I'll definitely be back on here soon!

Sounds like you are on top of things...It will either be the thermistors or too low of flow from your circ pump.

I would check to see if the pump is clogged, and replace the thermistors since you already have new ones.

If that doesn't work I would replace the circ pump. There is no real way to test it.

Thanks for the quick reply!

Since my post I have done further testing...
With no jets on, after breaker reset (both breakers this time!) first shutdown was 10 mins later.
Second reset took 5 mins to shut down.
Third took about 5 mins too, this time with the filter removed.

Since the last reset I have turned on one jet pump (filter back in) and it's been running fine for 45 minutes and counting...
leading me to believe that it's low flow thru the circ pump when the jets aren't moving the water. tomorrow I'll take it out and see if it's clogged or binding, unless anyone has a better suggestion!

Thanks for the help~

ok it ran without shutting down for 2 full hours. then the ready light actually came on! turned on a jet pump again to see if it would stay on and remain at ready status until morning. maybe flushing it with the rinse helped unclog the circ pump?? hmmmmm " title="Wink" />

Ok, today I opened the service panel and decided that it was time to replace the two questionable thermistors to see if that was the cause of the shutdowns.

Replaced the high limit one first, no problem. But the new Temp sender leaked when tight, so i had to scrape away the plastic flashing in the o-ring seat on it (leftover from the manufacturing process) and that fixed it. thanks for the extra headache, Watkins!

Got it back together and it's been running fine since 3pm today. so far no more shutdowns. I did notice some particles in the footwell that I know weren't there before I worked on the thermistors, maybe jostling the circ pump worked them loose? Ran out of time today, but tomorrow I'm gonna pull the circ pump and disassemble and clean it with CLR and see if the output plume changes. I studied the current size and volume of the plume of heated water rising from the drain in the footwell, so I hope to see an increase after reinstalling it.

I'm about to 'ohm out' the old thermistors... I wanna know for sure if they were good or bad. Hoping to find one or both out of range. Wait... what is the proper range of resistance? time to scour the manual. wish me luck!