Jandy LXI heater, shorted h2o sensor

mtesh73

Well-known member
Jul 14, 2015
82
Colts Neck, NJ
Hello everyone,
I searched and came up with 1 thread relating to this issue with good advice and followed it. I am now on my second sensor however. The heater is 5 years old and I first got the error message a month ago. I ordered a new sensor and replaced, immediately I got the same fault message. At that point I followed the diagnostic instructions of the last post by turning off the power, disconnecting the sensor then re-starting and the fault disappeared. So I ordered a second new sensor and installed yesterday. I went to run the heater this morning for the first time since yesterday's second install and got the same fault. I will follow the diagnostics with a multi meter this time. I wanted to check and see if anyone thinks it is possible that both new sensors were faulty? I will report back with multi meter readings after my daughter's 13th birthday party today.
Thanks in advance.
 

ajw22

Gold Supporter
TFP Guide
Jul 21, 2013
11,283
Northern NJ
This the thread you found?


I would check the wiring in the heater to see if any critters chewed on it.

When a temperature sensor is missing many systems default to a value. That is likely what is happening when you disconnect the sensor and the fault clears.

I doubt you got two bad new sensors.
 

mtesh73

Well-known member
Jul 14, 2015
82
Colts Neck, NJ
All wires seem intact. I performed the resistance test on the original sensor (submerged into 85 degree pool water) I took out and got an Ohm reading of 3.41 that reading should have been in the 8.20 range (so I am pretty sure that one is shot), I disconnected the new sensor from the board this morning, the pool temp is 85 which should result in an Ohm reading of 8.523, my reading was 13.99. This lead to the temperature on the heater control panel reading 95 to start and quickly climbed to 110 and counting, which at some point will trip the heater into faulting.

Any thoughts?
 

ajw22

Gold Supporter
TFP Guide
Jul 21, 2013
11,283
Northern NJ
All wires seem intact. I performed the resistance test on the original sensor (submerged into 85 degree pool water) I took out and got an Ohm reading of 3.41 that reading should have been in the 8.20 range (so I am pretty sure that one is shot), I disconnected the new sensor from the board this morning, the pool temp is 85 which should result in an Ohm reading of 8.523, my reading was 13.99. This lead to the temperature on the heater control panel reading 95 to start and quickly climbed to 110 and counting, which at some point will trip the heater into faulting.

Any thoughts?
Are you still getting the shorted fault or just bad temperature readings?
 

Pool Clown

In The Industry
Sep 5, 2008
2,011
Silicon Valley, CA
Im leaning toward a board issue. But first, scroll down to post #6 on the thread you linked in your PM and follow the part where you should plug into the board a fixed resistor and check the displayed temp. That will rule out another faulty thermistor. If the displayed temp reading begins to climb with a fixed resistor plugged in, you know a board is causing the fault.

This guy designed the boards Jandy still uses today for their automation.
 

mtesh73

Well-known member
Jul 14, 2015
82
Colts Neck, NJ
Many thanks. I am not an electrician so let me double check to make sure I follow. I can plug in a resistor with a value of 9.264 to the lugs on the board, then the reading on the LCD screen should register at 80 degrees?
 

Pool Clown

In The Industry
Sep 5, 2008
2,011
Silicon Valley, CA
Well, yes but you will need to know the value of the resistor, then see what the temp display should be using the chart in that other thread. Example: if you were to get a 10.0K ohm resistor, you should get a temp reading on the heater display of 77 degrees.
 

mtesh73

Well-known member
Jul 14, 2015
82
Colts Neck, NJ
I should have the 10k ohm resistor this weekend. It just dawned on me that there is also a 2 part sensor (high limit) on the plumbing on the right side near the rear of the heater. Should I be concerned about this part being bad and causing the fault? Or is the "shorted h2o sensor" fault only related to the temperature sensor (part R045600) found on the front of the plumbing? I replaced # 29 in below picture, could # 40 be the problem? I also don't recall a plastic sleeve coming out of the original sensor or getting one with the new sensor. What is the sleeve for?

1565977640478.png
 

Pool Clown

In The Industry
Sep 5, 2008
2,011
Silicon Valley, CA
If that sensor/switch were to open, you would be getting some sort of High Limit, HL, fault or something like that displayed. That sensor opens when the water temp exceeds the rating of the switch. Hot water opens the switch, heater shuts down, switch cools off and closes, heater re-fires and begins to heat again until the switch opens again.

Sleeve is like a clear "shrink tubing" on the sensor. You may or may not get it on a replacement sensor. It acts to keep temp uniform throughout the length of the sensor.
 

mtesh73

Well-known member
Jul 14, 2015
82
Colts Neck, NJ
Understood, great information.... thank you for explaining. I plugged the 10.0k resistor in, LCD screen reads a constant 75 and the the heater fires as it should. So if I am understanding the diagnosis correctly the board is OK and I got 2 bum sensors??
 

Pool Clown

In The Industry
Sep 5, 2008
2,011
Silicon Valley, CA
When you get the next sensor, plug it into the board and just let it hang there and start the heater. Make sure that you are getting constant temp displayed. If you do, go ahead and install the sensor into he header and repeat. If the temp display begins to rise more than one degree per hour (in pool mode) then something is up with flow throughout the heater.
 

mtesh73

Well-known member
Jul 14, 2015
82
Colts Neck, NJ
Haha. OK, I will give a try again. As a point of reference, when installing the new sensors I did let them "acclimate" to the air temperature for about 10-15 seconds. Once I saw the fault was cleared I installed. I will let it hang for sometime and run the heater as well. Stay tuned.
 

mtesh73

Well-known member
Jul 14, 2015
82
Colts Neck, NJ
Turns out I noticed a burn mark right below the orange chip on the right hand side of the board. When I went to install the new temperature sensor this message was displayed "universal controller, UI FW Rev: 1.8". I am guessing the board did not like having the 10.0k ohm resistor left plugged in.

20190820_154812.jpg