I may be inacurate regarding the Hot Springs... I don't recall if they have the air control knobs or not. I've had just one and have since vowed never to have another. An air control knob would be located within easy reach of an occupant, since it's purpose is to adjust the amount of air fed to the jets for "creature comfort".

Go ahead and do that check again once you get up to your max temp and let us know where you are at.

here we are just a few hours later and the tub is "quickly" approaching 98 degrees (we're at 97.5 now). this thing heats very fast. i'll run my tests in the next hour or so.

at this point i am going to guess that the heater is going to be cycled off. why do i guess this? because i believe - and i could be very wrong - if there were a heat-leak, it would slowly approach 98. it would struggle to get up to that top number. this thing is flying to 98. just an hour ago it was just below 95.

i am wondering if our attention should not be focused next on the temperature control knob/unit - which is "very" easy to replace. we'll know more after i test the voltage to the heater in a bit.

thanks again - i really appreciate your expertise on this matter.

ok, the tub has been holding at 98 for over 30 minutes. i tested the voltage output to the heater - and there was none. i rotated the temperature control knob and there was no click. i turned it back up to 10 (max) - still no click. about 10 seconds after i took my hand off the knob, i heard the click, and voltage began running to the heater again.

should i consider replacing the temp-control unit at this point?

yup I think that is where I would start at this point. Good thing you brought notice to the fact that you had it off a couple days and the temp was well below 98. Could have chased that ghost for a while.

yeah, something you said in a previous post turned the proverbial light bulb on in my head as to why you had me testing the voltage and that the current temperature played a roll in your comments. it all became so clear ...

now i'll go to the task of finding the right part for this older spa.

The "Unknown device" is a flow switch.... While heat is turned all the way up, unplug and plug in this switch- You should hear a clear "click" each time it's pluigged in and unplugged, just like you hear when you turn the heat up/down. You might have an intermittant flow/switch, flow switch relay.

Sounds like the heater, thermistor, and heater relay are working fine, so I'd start looking at the flow switch circuit first (For testing or replacement purposes, the flow switch relay is a 12v dc coil T-92 relay).

ALso- be sure your filters are CLEAN. A slightly dirty filter will not allow this unit to heat.

swine - thanks for the info. last night we figured out about the flow switch but it does not appear to be the problem. right now we've narrowed this down to the fact that no voltage it being sent to the heater at or above 98 degrees. i am looking into a new t-stat as it is topping out at 98 then shutting off the heater.

thanks

That's great, i thought i read that it was clicking when it has reached 98 (when turning the t-stat up and down), and the t-stat still had a little legroom before topping out? Is it still doing so? Or does it seem that 98 is indeed the max, ie it won't click once it has reached 98?

Thanks, and good luck

here's what's happening. if i unplug the spa for - say 10 minutes or so - then plug it back in the t-stat has "a little" legroom before topping out (it clicks the heat on at about 7 or 8 out of 10 on the dial). after about 5 minutes of running the heat, the t-stat has about a milimeter of legroom, and after 10 to 15 minutes, it has none - whereby turning off the heater. during this 10 to 15 minutes the heat rises about 1 degree, but consumes the remaining legroom on the t-stat exponentially over that 1 degree. presently i'm up to 99 degrees and the t-stat is maxed out w/no more heat being fed to the spa. i'm ordering a new t-stat now

Gotcha- when you say you're ordering the t-stat- do you mean temp sensor? (part number 38415) The t-stat is an electronic circuitboard- could be bad, but the thermistor is a more common failure after 10+ years, and much less expensive