Laars LX400 Pool Heater won't stay on

[ejbauer]

Laars LX 400 Pool Heater will ignite and burn for about 5 seconds, then shuts off.  Blower will start, run for about 1 minute while igniter burns, then flames are ignited.  Flames stay ignited only for about 5 seconds then gas supply shuts off.

Diagostic code is AGC (Automatic Gas Supply).  If it ignites and burns for a short time, it seems the igniter and gas supply are OK.  May be the flame sensor, but it looked like nothing was wrong.  It actually worked yesterday and heated the spa (about 300 gallons) once.  I ran some errands and when I returned it had the AGS error code.

[ACtechGUY]

Looks to me like that code most likely points to a flame sensing problem. Lightly sand flame sensor and clean all connections to sensor. Be sure to check/clean all ground connections as well.

Here is a link to the manual with troubleshooting charts.www.southshoregunitepools.com/resources/manuals/LXheater.pdf

[ejbauer]

I'll give that a try tomorrow.  It actually heated the spa tonight to 100 degrees.  However, it would not re-ignite when it got cooler, then showed the AGS fault code.  Kind of weird how it works, then doesn't.

[ACtechGUY]

sounds like a typical bad connection

[ejbauer]

cleaned the flame sensor with sandpaper.  heater ignited and heated pool like normal.  then when it tried to re-ignite, the blower ran, igniter lit, but the gas never burned and AGS code displayed.  wonder if the gas valve is an issue or it is not triggering because of some pressure issue??  water pressure is fine.

[ACtechGUY]

Check out page 42 in the manual section 10.4.3.7 "Gas Valve Voltage" for testing the gas valve circuit.

[ejbauer]

delayed response...away for 2 weeks.

i ran a cycle yesterday and it seems to work, but will try again.

[ejbauer]

tried again...will work for first cycle. When it tries to maintain temperature (relight), it cycles but does not ignite the flame.  Igniter works, will light flame for about 5 seconds, then stops (flame will not stay lit).