Jandy LX heater stops heating, but no codes

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N

ntxpool

0
Jul 7, 2007
80
Allen, Texas
My Jandy LX heater fires up and runs fine.......but after a while, it shuts down and stops heating.......but with no codes or error light. I noticed it stops at ~92 degrees. I have it set at 99 degrees, but can change it all I want and the heater won't come back on. If I wait a day, it will fire up again, but the same problem occurs.

I suspect a limit switch or something like it, but I would expect a error code. The maintenance manual is zero help, and I've googled all over the forum and web and can't find anything.

Any ideas?

Mike
 
Hi Dave,
Ok, I had some time to troubleshoot this afternoon. I fired up the spa and it immediately started heating...no problems.

1) The SPA gets to ~92/93 degrees and heating stops.
2) Heater tries to restart a few times. Then all of a sudden, it tries again and fires. Heating resumes. (I didn't have a chance to get a reading of the sensors during this.) During this cycle, i think the gas valve wasn't opening, but i could see the ignitor heating up.

However, once it reached ~ 98, it stopped heating again...no codes/warning lights.

3) Checked the high/low water temp limit switches for voltage (test from transformer lead to switch point on control board ~28VAC, per install manual): No voltage
4) Checked the exhaust and intake temp limited switch for voltage (test from transformer lead to switch point on control board ~28VAC, per manual): No voltage

I did verify, while the heater was working the first time, that voltage did indeed exist at the proper levels on the switches.
So the install manual says this could be a number of things, including a tripped limit switch, so I checked the switches one by one for continuity.

5) high/low water temp limit switches: continuity ok
6) exhaust/intake temp limit switches: continuity ok

Still no voltage and heater not firing, but the control board is green (on).

Ok, I'm stuck. The only other thing the manual says is that it could be the controller board in the heater. Any additional ideas? Once it rests overnight, it works ok again, until it heats up.

Thanks, Mike
 
If it's not a tripped limit then it's possibly a component heating up on the board and causing a open. It could be a broken land on the board or a weak or bad component. What I find strange is that it stops at almost the same temp every time. Have you checked the thermostat to see that it's still made?
 
Yeah, I checked the water temp via my Aquapure system (sensor in the pipes) and with a manual thermometer, and it never quite makes it to the set temperature (in this case, 100 degrees). When it tripped for good, the heater never came back on or even tried.....and the water cooled from 98 degrees down to 92 degrees before I called it a night and turned the system off.

The strange thing is: during this whole troubleshooting, I had the control board flipped upside down and outside the heater casing (to access the voltage test points). So the board was nice and cool.

I'm going to run another cycle today and recheck the voltage. I'm going to first disconnect all the control board connectors and then reconnect them. I'm wondering if there is a way to jumper voltage from the transformer pin to the sensors, to "fake" an all-good condition. This might confirm that something on the control board is not feeding the voltage (relay or?).
 
Hi Dave,
Yeah, i wouldn't normally recommend that either, but it's something I considered (I did a similar "jump" on my furnace years ago, to validate the failure of a high temp cutout).

However, I may have found the problem: the "SPA" dial potentiometer is flaky.

I pulled the LT400 heater controller this morning and checked all the solder connections, looked at components closely, etc......everything looked fine. So I got to thinking: what would cause the heater to think everything is fine (ie I have no error lights....all the sensors have error lights...and the sensors show continuity)? Only thing I could think of is if it thought the temperature was ok.

The Jandy/Laars LT400 has a control panel with a temp dial for "Pool" and one for "Spa". Since my LT400 is wired to the Aqua RS control center via a two wire hookup, those two dials really do nothing more than set an upper cutoff temp....the RS center tells it when to turn on via it's own temp sensors. My LT400 has always been set on the "SPA" side of control (but it doesn't matter....again, it's functioning in very basic "heat on/off" mode).

I fired up the SPA again.....let it heat up until it died....and then I tweaked the manual "SPA" temp dial down and up. "Click" went the relay on the LT400 controller board and heat started up. It stopped again at ~97.....but I tweaked it again.....and again, it started heating again.

Just for grins, i switched the heat mode to "Pool" on the LT400 (not be confused with changing to "Pool Heat" on the RS control.....that would change the valve configuration). Temp so far has stayed fine with the heat cycling on/off/on just like it should.

So looks like the LT400 controller is faulty....but just the temp dial potentiometer for "SPA". It was thinking that it's own temp setting had been met, so it shutoff....no matter what the RS control center is doing. This is why I was getting no voltage at the sensors.....they weren't activated.

Mike
 
That's exactly my plan....leave it on "Pool", if this is the problem. I need a few rounds of "heating from scratch" before I declare victory.

Finding a replacement pot/var resistor should be pretty easy, but I'd have to find one with the right value and also stem size to mount the knob on. I'll probably put it off and be lazy.

Mike
 

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I have EXACTLY the same problem. I have also measured the resistance across the thermistor and it is within 1 degree of the control system's reading. The SPA goes to 98 when set to 101 and then cuts off, no errors at all.

I noticed on the back of the heater control board that there is a J8 jumper "NO TEMP ADJUST", set to jumper pins 1-2, which may be "TEMP ADJUST". I wonder if switching the jumper to pins 2-3 means "NO TEMP ADJUST" and just heats all the time (when the kill switch allows it). This would mean that the heater's variable thermostats would be taken out of the equation. For safety, the hi limit switches still come into play.

I can't find any docs on what this jumper does. Any ideas?

If/when the POOL variable resistor doesn't work, I think a 10K Ohm resistor wired across the temp sensor terminals would work. This would fool the heater into thinking the water was always 77 degrees F. Opinions?
 
gswaybright said:
I know this is an old thread, but I have this exact problem. What was the ultimate solution? My Spa temp set to 102, but cuts off at 92-95.
Click to expand...

Has anyone found a solution to this problem? I have a jandy lite2 model LJ doing the same thing. Spa only heats Between 99 to 100 degrees when set on 104 degrees. Any help would be appreciated!

- - - Updated - - -

Any solutions to your issues. I am having the same issue. Thanks
 
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