Laars LT 250 does not stay lit

[millerwd]

Having a similar issue with Laars LT 250 (natural gas). It has worked fine for 13 years. This year it started igniting intermittently. Now it will not stay lit at all. The surface ignitor glows, the gas valve clicks open, the gas whistles through the orifices, the burners light, but the valve clicks off within 3-5 seconds and the blower increases to vent the gas. After three cycles the AGS (auto gas shutdown) error illuminates. So far I have:
Replaced the flame sensor
removed burner assembly, vacuumed and blown out the burners
removed, verified gas orifices are not blocked
tried to light in both pool and spa mode (better water flow in pool mode)
There have been no changes to natural gas supply line etc.

I have the manual and will work through the check lists but I thought there maybe someone on this awesome forum who has some ideas of what to try next.

 

[Dan-H]

I had a similar issue on my Laars Lx400, and fixed it twice with two different solutions.

First time it was a broken wire inside the heater right at a connector. It took a while to find and I'll be candid, I forgot which one it was but it was one of the sensor wires. I also forgot the error that was displayed as it was not very helpful.

Second time I traced it to the hi limit temp sensors. One of the sensors had corroded and stopped working.

I found the sensors were rather expensive, and read somewhere an entire harness for another unit contained the sensors needed for less money.

This one is the harness I bought, which would not work in my heater, but the sensors were exactly what I needed.

Amazon.com : Zodiac R0457400 High-Limit Wire Harness Switch Assembly Replacement for Select Zodiac Jandy Legacy and LXi Pool and Spa Heaters : Swimming Pool Heater And Heat Pump Parts : Garden & Outdoor

I removed the sensors from the new harness, installed them in my existing harness and this fixed my problem.

Not sure if this is it but it is another thing to try.

good luck,

Dan

 

[millerwd]

Thank you for the assistance. I checked all the sensors and even ordered a µA meter to confirm the 5-7 µA. Cleaned the burners etc. to get a good flame current. In the end a new ignition controller worked like magic. That was the last item on my list since the flame actually ignited with the old controller and it seemed to stop working intermittently, which is consistent with a corroded connector or failing sensor. This is my 3rd controller (first one went out on a lightning strike). The heater is 13 years old, so no complaints here. The controllers are getting harder to find, especially new).

Very good tip about the sensor wire harness. Thanks!