Jandy LT400N-L heater not getting to temp

[okkleiner]

I noticed this thread, but everyone on it over the years has the same issue I am having, but no fix posted:
Jandy LX heater stops heating, but no codes



I have a Jandy LT400N-L (10 years old). My temp is set to 97 and only goes to 89. If I set it to 104 it only gets to 96. I replaced the Temp sensor (thermistor), but same issue keeps happening. The heater will fire up just fine and show the temp rising quickly on the Jandy RS controller. Once it reaches temp the heater goes into cool down mode and on the RS controller the temp drops quickly. Then the process starts over. My assumption is that we are seeing a temp variance from when it is showing the heater temp reading while heating, but once the heater cool down starts it is reading the temp in the main plumbing from the RS controller.

Any suggestions would be appreciated. Thanks

 

[ps0303]

The RS controller can only read the that systems water temp. That sensor should be located in the plumbing between the pump and the heater. The RS doesn't know or read the water temp from the heater at all. The RS simply turns the unit on or off based upon what temp you set it to. You should always set the heaters temp to the highest point possible. That way the RS system has the full range for heating temps.

If you were to manually switch the heater on, what temp does it say the water is as compared to the RS system?

 

[okkleiner]

I understand what you are saying (I was trying to say the same thing above). The system is setup as described and has worked for the last 10 years (I am original owner). In the last few months I have been experiencing the issue.

The heater has manual dials like this:
http://www.aqua-man.com/images/row_num/22525.jpg
They were set to full heat from the start and have not been adjusted.

How does the system know when the spa has hit the desired temp (what thermostat tells it that it has hit the desired temp)? Is it built in to the heater (temperature sensor = thermistor) or sensor in the plumbing that goes directly to the RS control board? Thanks for your help.

As stated before it seems to be a problem that happens to this heater. Here is another thread (that eventually ge’ts hijacked without an answer) that Pool Clown seemed to elude that he may know:
http://www.poolspaforum.com/forum/i...andy-lx400-heater-problems-wont-light/&page=2
Pool Clown “Is it by chance heating to about a certain temp every time (not the set point) it begins to have the shut off problem?”

 

[ps0303]

Well the temp sensor for the RS system should be controlling the temp and when it sees the temp has reached the set point you set it to, it would turn the heater off. However, if the thermostat on the heater is set to a lower temp than the RS system, once it reaches temp it would shut the unit down. So assuming the thermostat on the heater is cranked all the way up and working right, the RS would be controlling it. You can read the resistance on the heaters temp sensor and that could provide you clue as to what it thinks the water temp is. Then compare that to the RS. They both should be pretty close. If one is higher than the other then I suspect that one to be the culprit.

 

[Pool Clown]

You mention that: "Temp rises quickly by the RS controller" and "temp drops quickly" Exactly how quick is the temp changing? When it rises, can you stand there and see the temp come up every few seconds? Is it the same with the cool down?

Typically, the pool should rise about a degree or two per HOUR. Same with the spa, only it will be more like a degree (or two) per MINUTE. If it rises faster than that, the heater is either plumbed backward (nothing has changed in ten years) or, you have a temp sensor going out, maybe even a by-pass assembly that has eroded or otherwise is beginning to fail. Have you been at the heater when it comes on and monitored it for banging or popping sounds just before it quits?

Does the heater give you and trouble lights on it's front panel? The fact that it heats up, shuts down, then begins the cycle again suggests that you are (the heater that is) having an over temp issue.

When the heater shuts off, does the controller in the house confirm this? or does it show that the heater is still on? If it thinks that the heater is still on, then the problem is in the heater. If not, then the controller is telling the heater to shut off, in which case the controller is the issue. either a bad temp sensor, or the thermostat is not set high enough. Remember, there is a thermostat for the pool AND a thermostat for the spa. Be sure you are setting the right one for what you want.

Given that you are the same owner for the last ten years, you probably have an issue with the controller and/or heater, and it isn't an operator error.