I have an AP-4 that was up and running fine even though I am only use a one speed pump (it's a retrofit). When I called Spa builders group they assured me that since I'm only using the pump as a circ pump because the jets have a separate pump it should work just fine. So what's my problem now? My heater started to overheat so badly that I actually melted the end of my pressure switch! I replaced the pressure switch and the unit runs fine for a few minutes and then blows the GFCI. It heats, so I'm pretty sure it's not the heater. Could it be the thermostat? There was an old post where one suggested feeling the heat tube to see if one end was hotter than the other but then the post just stopped. There seems to be plenty of pressure through the pump and as long as I don't turn up the thermostat, the pump runs fine. Good news as it's really cold for November in NJ. Any help would be really appreciated.

I a bit confused. You say the spa heats, but then you say the pump runs fine unless you turn up the thermostat. I'd recommend disconnecting the heater and trying to run everything else. The over heat may have damaged it.

As for why it overheated you may have had an uncalibrated pressure switch, a blockage in your line, or maybe a stuck relay. Whatever it is, you'll need the spa to be running without tripping the breaker before you can sort the rest out.

Start with the heater disconnected and give us an update from there.

And I thought I was being so clear. The heat starts to work (I can feel the tube get warm) and a few minutes later blows the gfci. If I don't turn on the heat, the tub runs for hours without blowing it.
Meanwhile, from where do I disconnect the heater? Just remove the wires from the element? Do I need to jumper them together? How does the circuit complete when I turn on the thermostat?
Thanks for your help.

Your thermostat is probably hooked into one of a few relays inside the box.

Is it throwing the GFCI or the High Limit (red button on front)? It is unusual for a heater to trip a breaker only after it is allowed to heat up. If you have an amp meter, check to see what the heater is drawing as it heats.

If it's the high limit then the heater is overheating either because there is insufficient water flow or the pressure switch is closed when it shouldn't be. Clean your filter, calibrate your pressure switch, and by sight make sure the water is moving when the heater is on.

I'm still in the dark here and starting to feel that I'll never soak again. Please bear with me, I really appreciate it. How do I calibrate the pressure switch?
I can't see the switch inside the box. I did pull the pump connection and the unit shut down right away. I can see the water flowing freely when the pump is on (heater or not). Filter is clear, no obstructions. I'm still where I was before. When I turn up the thermostat, the element runs for a few minutes, feels like it's overheating and within a few moments shuts off the thermostat.
If I push up the thermostat and call for more heat it will start heating again.
After a couple of tries, the hi-limit pops.
Can you tell me more about the relays? I still need to ohm out the heater, work sometimes interferes with the problem determination process. I have now changed the pressure switch (same problem), hi-limit (same problem), thermostat (same problem). I can't help thinking that when I jumpered it back to 120 from 240 I missed something somewhere even though the manual says that's all I have to do.

To calibrate it, attach an ohm meter or continuity tester with the pump on low. Tighten the adjustment screw until the circuit opens, then turn back a quarter turn so that it closes again.



What switch are you looking for inside the box?

How many pumps do you have, what type are they (make/model/horsepower), and which one is hooked up to the heater? A picture would be a great help.

Again, the only way for the heater to overheat like this without the spa getting very hot is if you have insufficient water flow through it. When you say it feels like it is overheating, is it hot to the touch or is it painfully hot to the touch and making funny, boiling noises?

It sounds like the thermostat is mounted to the heater itself with the high limit, so the thermostat is almost acting as a high limit, cutting off the heater when the tube reaches the set temperature. Open up the heater tube and make sure the element isn't resting against the tube where the probes are.



So the high limit is what's popping, not the GFCI?



Sounds like the relays are working fine, as is the heater. Changing the pressure switch without recalibrating it won't necessarily fix your issue, the high limit is doing it's job, and the thermostat is mounted to the heater so it's being fooled.

Again, a picture would be very helpful.

Well, after a long weekend, I'm back. Flow is very good and I'm back where I started. The pump runs fine as long as I don't turn on the heater. First the heater clicks off as if it's reaching temp. If I keep pushing it up the high limit does its job and shuts the unit down. NOT the GFCI. I pulled the pack and the element is not touching the tube anywhere. But the element seems so large and doesn't look anything like any element I can find on the internet.
I read somewhere that using a 5.5 element (in a 240 pack) can cause some units to overheat. Since the pack was recently converted from 240 to 120, I'm wondering if that is my overheat situation. (Grasping at straws here )
If it's not the high limit (changed already), not the thermostat (as Spa builders told me it was) (changed already), not the pressure switch (changed and calibrated)......I'm running out of parts here! Any thoughts are really appreciated.

5.5kw is standard for a 240v system. Switching to 120v should be giving you somewhere around 1.5kw. If your source electricity is 120v then a mistake in the conversion would lead to something not working, not overheating.

How hot is the thermostat allowing the tub to get before it kicks off?

I know this will sound crazy but the heater doesn't stay on long enough at this point to raise the temp. It will click off within minutes. The instant I turn up the themostat (even with the tub at 63 degrees now), the heat comes on, I can feel one side of the tube get extremely hot and then the thermostat kicks off. It works a couple of times like that until I can't turn the thermostat any higher and then the high limit shuts everything down. The only thing that makes sense to me at this point is that I REALLY appreciate your help.

You have a flow problem. PLAIN AND SIMPLE! You should NOT be able to feel any heat difference from touching the heater tube when the pump is running AND PROPER water flow is traveling through the heater. "Normally" the difference in temperature from the water entering the heater, to exiting the heater should only be about 1/4 to 1/2 degree.