Jandy LT heater not reaching set temp- Hi Limit trips (and now Air Flow trips)

bproosow

Bronze Supporter
Apr 8, 2014
51
Auburn, CA
Hi all! I have a 14 year old Jandy LT400 that we really only use to heat the spa. It worked fine the last time we used it, I guess it was a few months ago. Went to turn it on the other night and it started heating up as usual, but stopped around 87 degrees. I went out to the heater and found the Hi Limit and Service LEDs flashing. I found the Jandy troubleshooting flowchart online and went through that. I am getting appropriate voltage to and from the Hi Limit switches when the heater initially comes on (it runs for probably 15 minutes before tripping the light). When it trips, I'm not getting voltage out to the switches. According to the flowchart, this apparently means the GUI/control board is bad, but I'm not convinced. I'm concerned that it may be a flow issue and these components are doing exactly what they're supposed to do. Any heater experts out there that can help me out? TIA!
 

ajw22

Gold Supporter
TFP Guide
Jul 21, 2013
20,329
Northern NJ
First thing to do is check your filter pressure and water flow to the heater. Low flow causes overtemp and Hi-Limit shutoff.

What is your clean filter pressure? What is your filter pressure now? When was the last time you cleaned your filter?
 

bproosow

Bronze Supporter
Apr 8, 2014
51
Auburn, CA
Filters were cleaned last week. I want to say the baseline after cleaning was around 35 PSI. I'll have to double check that though. Flow looks good, pulling harder from the skimmer than prior to cleaning. However, that's when it's pulling from the pool. I haven't checked what it does when it pulls from the spa. That would be very telling if the problem only happened when using it in spa mode. I've never used it to heat the pool since I have solar heat. I wonder if maybe leaves got jammed up in the spa floor drain?
 

ajw22

Gold Supporter
TFP Guide
Jul 21, 2013
20,329
Northern NJ
35 psi is very high for normal filter pressure. It is usually under 20.

Try pulling your cartridge out and running your pump and heater. Note what the filter pressure is and if your heater works normally.

You could have algae in clear water that clogs a filter fairly rapidly.

Leaves in the suction side would not cause high filter pressure. It would show as lack of water in the pump basket and the pump running dry and getting insufficient water.
 

bproosow

Bronze Supporter
Apr 8, 2014
51
Auburn, CA
That may have been with the solar on, and the panels are probably 40 feet higher than the pump, so that may be why the pressure was so high. On the other hand, it's plumbed so everything runs through the heater, so a blockage in the heater could cause the high pressure as well. I'll have to take a look in the morning. Thanks.
 

ajw22

Gold Supporter
TFP Guide
Jul 21, 2013
20,329
Northern NJ
If you want more help post pics of your pool equipment.

Lower your filter pressure and you will get more flow and probably solve your heater problem.
 

bproosow

Bronze Supporter
Apr 8, 2014
51
Auburn, CA
I just ran out there to check it just in regular pool mode, no heaters on and the pressure is about 21 PSI. Put it in spa mode and got 24 PSI.
 

bproosow

Bronze Supporter
Apr 8, 2014
51
Auburn, CA
I went out and ran the heater on pool mode (with the lower pressure) and it ran flawlessly. It looks like I have some bits of leaves packed into the floor drain in the spa. I'll go out there later and clean it out, but it looks like that's the culprit.
 

bproosow

Bronze Supporter
Apr 8, 2014
51
Auburn, CA
Soooooo.... That wasn't it. I definitely did have a flow problem. It was at 21 PSI, then the next day back to 35. I went through an extensive process of elimination, tried running without filters (no change). Turned out to be a broken check valve between the filter and the heater. The flap had broken off and was blocking the outflow to the pool. Unfortunately it was the old non-serviceable style, so I had to replumb the section between the filter and the solar diverter valve. Now that the flow issue has been resolved, the pressure is right around 20 PSI for the pool and 21 PSI on the spa (makes sense because there are fewer returns). Unfortunately the heater issue still remains. It seems to pretty consistently kick off around 87-88 degrees. I'm thinking I might just try replacing the limit switches, but I'm curious if anyone has other ideas about what might be the culprit. I'm attaching a diagram of the pad to help make sense of the setup.
 

Attachments

bproosow

Bronze Supporter
Apr 8, 2014
51
Auburn, CA
I went back down to give it another look, and I'm no longer getting the hi limit light. Instead I'm getting the air flow light. What is the troubleshooting procedure for checking the airflow?
 

bproosow

Bronze Supporter
Apr 8, 2014
51
Auburn, CA
Final post on this, primarily for the benefit of anyone who has these issues in the future. The system is about 14 years old now, and it turns out that I had multiple problems, all of which affected the heater operation:

First was a broken check valve. The flap broke off and was swirling around inside the valve (since it was the old, non-serviceable style, I couldn't see it). This explains the erratic pressure measurements. Since this valve was in the wrong place to begin with, I just replaced this section with regular pipe. There was no check valve between the heater and salt cell, so my new Jandy check valve went in between them, which should prevent corrosion issues in the heat exchanger.​
Next, the airflow error. I checked the vent on the top but there was no debris there, and cleaning it did not fix the problem. This problem was resolved by cleaning the venturis. I used a brush for cleaning refrigerator coils, it's maybe 1.5-2 inches wide and about 18 inches long. This was the absolute perfect tool for this job.​
After fixing both of those, I still got a hi limit error (after fixing the plumbing it would go back and forth between airflow and hi limit errors). I removed both of the limit switches and found that one of them had some corrosion. I scraped it off and cleaned it up with some sandpaper, reinstalled, and now everything is working fine.​

I hope this will help someone out down the road!