I purchased a Serenity Spa in June of this year and it has been working fine until about 2 weeks ago. I first noticed it seemed to be running every time I went by it. The temp will not get up to 101 degrees that is set on the control. If I lower to 80 degrees the temp will be maintained. Also, I can turn the spa on high speed and the temperature will reach the preset 101 degrees. Of course, I have to do this several times, since the high speed times out after 15 mintues.

It seems that the heater is not working when the pump is on low speed. I don't think there is a problem with the thermostat, high limit sensor, or flow sensor, since the unit will turn off after getting the temp to 101 on high speed. Sounds to me that there is a problem in the circuit board.

The spa has the Balboa Lite Digital control system.

Sounds to me that the flow sensor is defective.

The only purpose of it is to ensure that there is water flow before turning on the heat. It has nothing to do with turning off the heater once temperature is met.

You can confirm this if you have adequate flow (confirmed) and jumping out the flow switch (as a test only) to see if the temperature will increasing.

I have the exact same problem. I have jumped out the flow switch and there is no problem there. The heater light stays on along with the low setting on the pump 24 7. The heater light will go off when I break the jumper on the flow switch. Any other suggestions? Catsailr, did you ever find a solution?

Just out of curiousity, have you checked for power across the two heater terminals during circulation pump cycle (heat cycle), low speed, and high speed operation?

Please post the results.

The power looks good in high or low speed. The heat cycle I don't know about because the pump and heater run 24/7. I don't have a mechanical timer to adjust that. When I set the temp low, the heater shuts off (verified with multimeter, also heater indicator light shuts off) but the pump continues in low speed. This spa is new to me, the previous owner states that it heated up fine for him. It is a cal spa circa 1996. Is is possible I have enough flow to maintain temp around 87 degrees and not overheat, but not enough flow to heat up the spa without turning spa to high?

I am a little confused on how you can check for power at the element when in low speed or high speed, but you can't check it during circulation/heating. Regardless if the circulation pump runs all the time, the heater is still controlled by a thermostat and turning it up will engage the circuit to apply power to the heater.

The point I was attempting to make is that if you have power at your element when in heat mode, and still no heat, you will need to replace your element.

Based on the information at hand, my theory is your 87 degrees is where the tub will heat to from the heat generated from the main pump motor running. I suspect your heater element isn't heating at all, at any time. There is no provision that will limit the temperature based on variable flow rates. Either there is enough flow, or not, and the heater is on, or not.

Do a little more checking with that element power AT the element, and see if you have power there at any time the thermostat calls for heat, with the jet pump off, in low, and in high.

Sorry, let me be a little more specific. I am getting power at the element during circulation/heating. I am also getting power in high speed. What I meant to say is the circulation/heating cycle appears to be constantly running, even when I turn the temp down. I give it 20 min, thinking it will turn off eventually, but it never does. Maybe this is normal for my tub, but I was under the impression that most tubs will turn the pump on and off according to temp.
I can heat my tub to 100+ degrees, but only if i turn on the high speed jets. Could I be generating that kind of heat from just the pump? I have to turn on the jets every 15-20 min when the timer kicks them off, but if i do this for a few hrs, it gets up to temp. When that happens, the heater will turn on and off, mostly on unless I turn on the high speed jets again. I only heat 3-4 degrees an hour, which I think is normal for a 220v tub in high speed. I am down to 84 degrees just using circulation cycle. It would maintain temp at 100+ when the weather was warmer, but now that the temp has dropped (20 degrees at night) the tub temp is dropping. Cover and insulation appear to be in good shape. Ohms=12 at element.
Any suggestions? Color me confused!

Starting over...

Has anything been done to the tub prior to this event happening?

Generally tubs do NOT heat on high speed unless they are specially set up that way. Very few are, since they draw a LOT of power. Also, a 240V tub will heat about a degree every 7 to 10 minutes. If you have power at the element during the heat cycle, it will heat unless you have a bad element. Do not rely on the indicator light on the panel for determining wether you have power or not.

verify you have 240v across the terminals of the element during the heat cycle. I am willing to bet you do not.

In a well insulated tub, the temperature can rise when in operation. Arctic spas uses this as their primary heat source, as do soft tubs.

What brand and year is your spa? What is the control system?