Jandy LT 400 heater issues

[panzerwagon]

Long time listener - first time caller....


I've seen the same behavior with the same heater. I'm also stuck at step 3 of the troubleshooting guide.
Powers on and cycles each individual LED on - which is presumably a power-on-self-test. It's getting power, and getting the on signal from my pool controller. As OP noted, I've got 28V at the transformer - which is either normal because it's unloaded, or abnormal... and ?

My 10k thermister reads what i believe is right (10k at 72deg and 8.5kohm at 85 degrees water temp) and I've replaced the controller board. Behavior is the same. No voltage at the 3rd wire. Are there any alternative / external problems which aren't noted in the guice, but could prevent these contollers from deciding to come on?

Thanks.

 

[ajw22]

Welcome to TFP.

Exactly what model heater do you have?

Post pictures of your heater.

 

[ajw22]

Long time listener - first time caller....


I've seen the same behavior with the same heater. I'm also stuck at step 3 of the troubleshooting guide.
Powers on and cycles each individual LED on - which is presumably a power-on-self-test. It's getting power, and getting the on signal from my pool controller.

Does the fan blower start running?

Did you replace the thermostat?

 

[panzerwagon]

replaced the thermostat (controller board), yes.
Fan blower doesn't start.

The 24V isn't passed through any of the safety switches. The troubleshooting guide says that means that the thermostat's not calling for heat, and the board's not trying to turn on. Based on the measurements I made with a meter, it seems the thermistor's working properly though. Maybe i'm wrong about that.

 

[ajw22]

I think the thermostat is separate from the controller board.

Show me pictures of the heater and the controller board.

 

[panzerwagon]

 

[ajw22]

Based on the measurements I made with a meter, it seems the thermistor's working properly though.

The thermistor is not the thermostat.

The two knobs are the thermostats. Are they on the controller board?

Did you try the switch below in both POOL and SPA setting?

 

[panzerwagon]

Understood. The thermistor is the temp sensor in the water flow, and the thermostat is the circuit board on the back of the Jandy heater control panel above with 2 knobs. These 2 knobs are connected to 2 potentiometers on the board.

Cycling power on the system causes the Jandy heater control board to do the self-test where it cycles through all LEDs for for 1sec individually. Touching the pool/spa button doesn't change anything. No lights. No change in behavior.

The heater on/off control signal comes from the Jandy Aqualink control unit at the far right, and it's present at the Jandy heater control board when I set Aqualink to "spa mode" and "heater on". When it set spa off in aqualink, that control signal goes off. So the problem isn't the larger pool control system.

When this control signal is present at the heater control board, the 24v is passed through to the heater control board, but the heater controller doesn't attempt to go any furnther. 24V on pin1, pin2, but not on pin3. The Jandy troubleshooting guide says it's the thermistor or the heater controller board. I changed the Jandy heater control board for a new one, and behavior is exactly the same.

Like I said before, the thermistor seems to also have correct resistances vs temp for a 10k thermistor. To ground, the thermistor reads about 1mohm, so it's not shorted, but it's not open circuit either. I can change the thermistor but I'm confused that it seems ok...

 

[ajw22]

Where did you get the new control board from?

Let's have @swamprat69 have a look when he wanders by.

 

[panzerwagon]

eBay - so it’s admittedly used not new.

 

[swamprat69]

As I understand it when troubleshooting you get through the first 2 steps and have 24V between the red and green/yellow terminals on the transformer terminal bar. When checking the 3rd step "check safety loop" , you get 24V on the first black wire and the second white wire but do not have 24V on the third white wire. Is that correct?

 

[panzerwagon]

As I understand it when troubleshooting you get through the first 2 steps and have 24V between the red and green/yellow terminals on the transformer terminal bar. When checking the 3rd step "check safety loop" , you get 24V on the first black wire and the second white wire but do not have 24V on the third white wire. Is that correct?

That’s exactly right. I tried another thermistor and even put it in a glass of cold waterlast night. No change in behavior. When I unplugged the thermistor from the board, it starts flashing a temperature sensor warning LED. That behavior seems rational….

 

[swamprat69]

It is difficult to see on the colored troubleshooting guide because it is covered by the white circled #3,but the connection between white #2 and white#3 is through the "call for heat relay" on the circuit board/controller. I am attaching electrical that does not have the white cicrcled #3. It seems that you are not actually calling for the heater to heat ( thermister, circuit board/controller or "call for heat" relay problem ). You could confirm this by using an alligator test jumper https://www.amazon.com/Alligator-El...37&mcid=e5c177e890483a79b66b82dc672f63f4&th=1 with a couple sewing needles to jumper between white #2 and white #3 to see if the heater will start and run. If it does run and heat and the thermister is good it would seem that the problem lies with either the circuit board/controller or the "call for heat" relay. Don't know what you used to pay for the board on Ebay (paypal?credit card?), But I would start a return for " not as described or not working". Always be careful when purchasing parts on Ebay or from Amazon third party sellers as returns can sometimes be difficult. I recently purchased a "display" for my 18 year old hayward ng heater that was listed as 100% working, but when I installed it, I found that of the 3 led lights (standby/pool/spa) the pool light was not working but since I know which of the three lights is not working and how the lights cycle it is a minor inconvenience.

 

[1poolman1]

eBay - so it’s admittedly used not new.

The board you got is probably bad as well as your old one, sorry. Those boards haven't been made in at least ten years, probably longer. My LT did the same thing.

 

[panzerwagon]

Man, you guys are good. I shorted pins 2&3 and the heater kicked on. I have 2 bad Jandy heater controller boards.

Now I understand that the 24v has to pass through the thermostat and all the safety measures before it’ll turn on. This controller board is the thermostat but it also handles the diagnostics which puts a light on if each fault occurs.

Here’s a question… This pool system is setup such that the heater’s thermostat is always left set to max. The heater is a slave - driven with the on/off control signal from and temp control done by the larger Aqualink pool control system…

Now, it seems to me that I can conceivably leave this jumper shorting across the Jandy LT400’s control signal, let the Aqualink manage temp & on/off, and that all the heaters primitive safety features are still in circuit. The fireman’s switch, the flow switch, etc… with the thermostat being set to to max all the time, it was kind of already doing this.

I won’t have the LEDs on the front of the heater to tell me which safety feature is preventing me from starting one day, but until that day, it should work well - and importantly - safely enough.

The obvious arguments against are “insurance” and “that’s not how it’s supposed to work”,
But in principle, am I correct?

Thanks again