Jandy JXi - Incorrect Water Temp

[jonahls]

4 year old Jandy JXi 400N, used with a pool, is all of a sudden showing erroneously high/incorrect water temperatures in the 130F to 135F range (actual water temp is probably 78-82).

Checked water temp sensor and I think it checks out OK. Resistance was ~10.5K Ohms which slowly dropped to ~9.8K or thereabouts after I ran the pump for a few minutes (I don’t remember the exact reading). Tagging @ajw22 since he seemed to be knowledgeable about this type of situation.

With the temp sensor disconnected from the board the heater shows temp as 113F-115F. I put a pair of 5k Ohm resistors in series, that measured 10.13K Ohms together, across the water temp sensor inputs on the controller board and the heater shows the temp as ~130F.

What’s my next step? I am guessing this is a board issue? Do I have to replace the board? Or can these boards be repaired - like maybe it’s a bad SMR or cap that I could attempt to replace?

If a new board is the solution, do I need one with the exact same assembly #? Or is a different final letter OK, or what? There are some used ones avail for a lot less than new…



Any help appreciated!

Thanks,
Jonah

 

[ajw22]

You did the basic thermistor troubleshooting and it points to the board.

Maybe @PoolGate @setsailsoon knows about that board replacement.

 

[PoolGate]

What temp sensor did you check? Do you have aqualink?

 

[setsailsoon]

I'd go down the same road @PoolGate is. Are you sure the temp sensor is the one your heater is reading? It's pretty rare for the boards to fail without an obvious burned up component. If you do go the replace route there was one I dealt with and found to be very reliable. Let me see if I can find them.

Chris

 

[jonahls]

What temp sensor did you check? Do you have aqualink?

No aqualink. I checked the temp sensor that is in the inlet. I don’t think there’s another sensor other than the safety/overtemp ones, is there?
I wasn’t getting a fault so I don’t think it is either of the overtemp sensors.

 

[jonahls]

I'd go down the same road @PoolGate is. Are you sure the temp sensor is the one your heater is reading? It's pretty rare for the boards to fail without an obvious burned up component. If you do go the replace route there was one I dealt with and found to be very reliable. Let me see if I can find them.

Chris

Yes, I’m sure the sensor and sensor input I tested is the one driving the display and controlling when the heater cycles. When that input is floating free the temp shows as 115F and with a 10K across the input it shows as 130F. With less resistance the temp shows as even higher until the display indicates a “Fault - High Water Temp.”

It’s hard to see if anything is burned on the board without removal, lots of surface soldered tiny components hiding behind wires.

Best I can find is a used board on e-bay (with the same Assembly number) for $100 which seems reasonable. Assume it was salvaged from a heater that died for other purposes.

Any other leads on a source for a replacement would be appreciated. Thx.

 

[PoolGate]

Honestly I would replace the sensor before the board.

 

[jonahls]

Honestly I would replace the sensor before the board.

But it reads 130F with a 10k Ohm resistor across the sensor connector, so how could it be the sensor? Shouldn’t it read ~72F with that level resistance?

 

[PoolGate]

The sensors go out a lot the boards not so much. Sensors are cheap too. If it's not that you can always replace the board later.

 

[setsailsoon]

They also normally fail high. If this doesn't work you'll have a spare and you'll need it sooner or later.