Jandy LXi 400 heater displaying "Fault - Shorted H2O Sensor" error message

AaronGo

LifeTime Supporter
Dec 8, 2011
135
Houston, Texas
I have a Jandy LXi 400 heater (along with the Aqualink PDA-PS4 system) and the LCD screen on the heater is displaying a "Fault - Shorted H2O Sensor" error message. The entire system is a little over 4 years old.

I called Jandy and they said it's likely one of two things:

1. The temp sensor is bad

2. The "board" in the heater is bad

I am hoping it's #1 but I am curious what I can do to troubleshoot this. Jandy won't tell me much to do except "call a service company".

Can I bypass the sensor by connecting the two wires on the temp sensor to see if the error message goes away? I don't care to spend $50 on a new sensor in the event that is not the issue or somehow the new sensor is damaged due to another faulty component. Any ideas on how to troubleshoot are welcome.
 

Pool Clown

In The Industry
Sep 5, 2008
2,016
Silicon Valley, CA
Re: Jandy LXi 400 heater displaying "Fault - Shorted H2O Sensor" error message

Thermistor test = Temp sensor test
Step 1 measure resistance. If resistance is infinite, stop test, sensor has failed.
Step 2 Come to terms with being 50 bucks lighter.

Seriously, if your temp sensor is ok, you should get an ohms reading somewhere between 7.6K (around 88 degrees) and 11.9K (70 degrees).

If your panel is reporting a SHORTED sensor, it could also be chewed wire INSULATION between sensor and board! A severed or chewed through wire would give you an OPEN fault.

o
 

AaronGo

LifeTime Supporter
Dec 8, 2011
135
Houston, Texas
Re: Jandy LXi 400 heater displaying "Fault - Shorted H2O Sensor" error message

thanks for the detailed reply. I will take these first few steps this weekend and see what the results are.
 

AaronGo

LifeTime Supporter
Dec 8, 2011
135
Houston, Texas
Re: Jandy LXi 400 heater displaying "Fault - Shorted H2O Sensor" error message

I finally tested the water temp sensor and it appears to be fine. Below is the pic of the multimeter results @ ~80* F

So I need to see if the wire going to the heater has some short in it. Otherwise its something else.

 

AaronGo

LifeTime Supporter
Dec 8, 2011
135
Houston, Texas
Re: Jandy LXi 400 heater displaying "Fault - Shorted H2O Sensor" error message

BTW, I think I was testing the wrong water temp sensor at first. I thought the water temp sensor going to the Aqualink box then sent info to the heater. But the heater has its own water temp sensor. The resistance reading was only ~1k, which would be true if the water temp was really high.
 

Pool Clown

In The Industry
Sep 5, 2008
2,016
Silicon Valley, CA
Re: Jandy LXi 400 heater displaying "Fault - Shorted H2O Sensor" error message

You can check if you replace the sensor with a resistor that has a value that would correspond to valid temp and see if the heater fault goes away, and the heater fires. Then you could confirm a bad sensor.

OR

Since you are getting a SHORTED fault, disconnecting the sensor from the board should result in a OPEN fault. Or at least the shorted fault goes away, verifying that the board is ok. But if you remove the sensor from the board and you still get the shorted fault, the board would be suspect.

VERY IMPORTANT: Disconnect power from the heater, disconnect the sensor, then power the heater back up. This will ensure the fault is cleared, the heater will reboot, and re-check for new faults.