I have an ap-1400 which was retrofitted into a Jacuzzi. Everything works fine except the red push button breaker keeps tripping. I am guessing from my reading in the forums my problem is the high limit switch. I have read the air intakes need to be fully open and this did seem to help a little, but not entirely. With the warmer weather, this thing is really tripping several times a day. In the cold weather it would sometimes go for days before tripping. I'm not entirely sure what to replace or what adjustment I could make. There are three sensors I can find. There is a sensor which goes into a pipe next to where the water flows. There are two sensors attached to the metal chassis where the heater element is installed. I don't know which sensor does what job. Is there an adjustment like a variable resistor I can adjust or should I just replace a sensor? Thanks for any and all input.

the hi limit sensor is one of the two located on the heater chassis (you can follow it all the way to the red hi-limit button), the main thing to remember is that if you have improper water flow through the heater the housing will become super over the span of a few minutes to a few hours and will make that hi-limit pop...so the trick is to be at the system when the hi-limit pops and then literrally feel all around the heater tube to see if it is very hot (it should be the same temp as the water), provided the tube is ok then all you have to do is replace the hi-limit.

http://spapartsnet.com/cgi-bin/cs/index ... &pd=HL2101

I had to clean the tub and while I was at it decided to clean the filter as well. The filter was only a couple of months old and I didn't think it could be all that bad. Turns out it was pretty bad. After cleaning the filter I no longer had shut-off problems. I assumed it was a water flow issue due to a clogged filter. Since that time I have cleaned the filter everytime I drain the water. I thought I was on top of things, but then had another problem. Couldn't get the tub to heat at all. I realized then the pipes were air locked and no water was passing through. I managed to get the water moving and everything was working again--I thought. My current problem is the heater doesn't seem to turn on by itself anymore. I can flip a switch on my heater box and it will heat, but it constantly heats until the high limit is reached and then the reset switch kicks in. By this time the water really is hot (108 or so). I clearly still have a lot to learn about maintaining my spa. My current question is does anyone have a users manual for an AP-1400? I don't know what the on/off switch on the control box is really for and I don't know how to use the timer switch. Thanks.