I have a used '98 Hot Springs Sovereign that I just had hooked up. After filling the tub and powering up the Power Light kept flashing. Per the manual and posts here, I cycled the power off and on to reset the High Limit Thermostat.

That didn't help until I accidentally left it like that for about half an hour. When I then cycled power once more the light stayed on! Jets flowed!! Joy!!

Having let it sit for 24 hours though I see that the tub is not getting warmer. It is around 60 degrees, covered. Both breakers are okay. Is there a way I can see if the heater is actually working? Searching threads here it seems like the first step I should take is to check the ohms on the thermistor. What and where is the thermistor?

What else should I test?

Thanks!

reset the heater. More than likely, you have a heater with a reset button on it. If the heater you have has an oval bend of stainless steel, the button in on the black base, look for the sticker mentioning so, the button may be on the back side of the base. You'll feel it, it's about 1/2 inch in diameter and is rubber, but it's flush. Press it with a round head screww driver, or eraser end of a pencil. If your heater is an all black, retangular shape, the reset button is ontop in between the 3/4" clear hoses, under a piece of tape.
110v spa will heat at 1-3 dgrees an hour
220v will heat at 7-10 degrees an hour.

check it after an hour or two to see if temp is up.

Before you check the thermistors, check the small, 24 circ pump for proper flow. A faulty circ pump will allow the high limit to trip, then it might remain warm enough to fool the temp sensors into thinking everything is OK.

Since the physical high-limit is still maybe tripped on the heater, re-setting it might lead the red-light to flash again--->points to bad circ pump.

If flow is good, probably bad thermistor

Thanks for both of your replies. I tried the heater reset last night and hour later the temp had gone up 5 degrees. Got up this morning and it's now at the temp I had set it for.

Thanks for your help!!

Now I'm off to learn about water chemistry and get this thing ready.

YAY!

Keep a watchfull eye on that circ pump though- that high-limit tripped for a reason...

Enjoy!

Swine's right. One last thing, if it's been longer than 3-4 weeks since you've CHEMICALLY cleaned filters,----do it. A dirty filter one the grey standpipe will restrict flow to circ. pump, causing a low flow through heater and possibly setting off the high limit.

When say CHEMICALLY cleaned are you referring to the Muriatic Acid treatment I read about here or just using the cleaner/degreaser I have now?

muriatic acid solution, if at all, should only be used AFTER a cleaner and degreaser solution.

soaking in muriatic acid solution first sets the body oil in the filter material. permanently.