I have a LAARS LT 400 natural gas heater for the spa and pool. About a month ago I turned the heater on to use the hot tub and the temperature never got over 80. I had a pool guy come out and he said it was either the flame sensor rod or the thermistor. He changed the flame sensor rod and it did the same thing so he said it was the termistor. I replaced the thermistor over the weekend and it still only gets to 80. Any ideas on what else the issue might be? I have no error lights on the top.
LAARS LT 400 Heater
- Thread starter thabeezer
- Start date
Pool Clown
In The Industry
Do you have separate automation that controls the heater from in the house? Or do you set the temp from the front panel of the heater itself?
Pool Clown
In The Industry
I dun know... It may be different where you are, although i dont see how geography could affect hi limits, but i just don't get hi-limit failures... at all. I was going to say a temp sensor with a wonky resistance. If it is truly a Laars heater, its old, and doesn't have a temp display but rather dials where you wouldn't know what temp the sensor is giving the control.
Disconnect the temp sensor wires from the control and see what the resistance is. That would rule out the sensor. Unless it is really old, and all you have is a bulb. Then you could see if the thermostat is opening the circuit (at 80 degrees) and shutting off the heater.
Disconnect the temp sensor wires from the control and see what the resistance is. That would rule out the sensor. Unless it is really old, and all you have is a bulb. Then you could see if the thermostat is opening the circuit (at 80 degrees) and shutting off the heater.
The poster said it is a Laars LT. Here is a link to the manual, https://www.parts4heating.com/v/vspfiles/images/pdfs/JandyLXLT.pdf It should have a digital display on it. Hi Limits are another sensor that can go bad for any reason. It happens. I don't disagree either that it could be a temp sensor. I would think that with a digital display it should be displaying an error on it.
Are the burners lighting like they should be and staying lit? If so, it is/was not the flame sensor. Flame sensors as a rule do not need to be replaced, only cleaned. If it was indeed the sensor then there would be no lit burners. I agree with the others that there may be something going wrong in the temp controller. Do you maybe have something programmed into the controller to limit this temp?
Just so happened that today I got a call on a Jandy LXi unit. Guy said it heats to 85 even though it's set at 101. Display was showing a Hi Limit error. Here are what the limits looked like. The right side is the hi limit and it's all rusted and corroded.
