Jandy LXI 400P heater: replace water pressure switch?

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agonista

Active member
Jun 21, 2023
36
Tampa, FL, US
i have a jandy lxi 400p pool heater from roughly 2008 that will not start.

the history is that this heater did not work when i attempted to use it about 1.5 years ago, so i figured out that the low voltage cable connecting it to the aqualink rs control system was bad. after replacing and reterminating the wires for this connection, the heater worked for the next ~6 months. the heater is refusing to start again, presumably for different reasons that the first time because i've confirmed the low voltage connection between the controller and the heater is live.

i've searched the forum quite a bit to self-educate and found the extremely helpful wiki entry for jandy lxi heaters. from this page, i followed it to the jandy troubleshooting guide with the wiring diagram for the lxi heater series. i have followed these instructions and checked the first few steps, but i have found that at step 5 (page 6) that if i don't see 24 vac between the water pressure switch line and ground, it says

"Do a Back Pressure Test, if pressure is higher than 2 PSI, replace Water Pressure Switch, if less clean filter, baskets or repair pressure problem"

i'm guessing i have a bad water pressure switch, but i would like to confirm that before ordering a replacement part. i couldn't find documentation on how to perform a back pressure test and have no idea how involved this is.

input appreciated, thanks for reading!
 
Start with using a multimeter and seeing if the WPS is open when you have no flow and closes when you have flow.
 
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ajw22 said:
Start with using a multimeter and seeing if the WPS is open when you have no flow and closes when you have flow.
Click to expand...
i have a diverter valve that can bypass the heater and a check valve that allows me to see flow to the water heater. both when the check valve is open and closed (flow and no flow) as a function of my changing the diverter position, i see 0 vac between the ground (yellow wire) and the switch sensor (grey wire).

i am also having a new problem, which is that i seem to be unable to use the aqualinks rs controllers (4 button at spa and lcd inside house) to turn off the spa and heater.
 
agonista said:
i am also having a new problem, which is that i seem to be unable to use the aqualinks rs controllers (4 button at spa and lcd inside house) to turn off the spa and heater.
Click to expand...
scratch that, i've managed to figure this part out (had to hit a button on the heater control panel).

oh, an added challenge - afaict, the little lcd display on the heater itself is busted. i'm not exactly keen to pay $500 to replace what is effectively a beeper display lcd.
 
agonista said:
i have a diverter valve that can bypass the heater and a check valve that allows me to see flow to the water heater. both when the check valve is open and closed (flow and no flow) as a function of my changing the diverter position, i see 0 vac between the ground (yellow wire) and the switch sensor (grey wire).
Click to expand...

Use the OHMS continuity function on your multimeter.

Don't turn on your heater. Just disconnect the wires from the WPS and check if the WPS opens and closes when there is flow.
 
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agonista said:
i am also having a new problem, which is that i seem to be unable to use the aqualinks rs controllers (4 button at spa and lcd inside house) to turn off the spa and heater.
Click to expand...

You have an old heater.

You have to decide when it is time to stop throwing new parts in it as other things break.
 
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