LAARS LIT2 Heater Problem

check gas pressure and the size of your line if too small a line and too long a run from the meter it will run out of gas in line then line fills back up heater fires and drains line again

see if 24 volts ac to the brown and yellow of the gas valve if voltage need new gas valve if no voltage need new fenwal

This error is Automatic Gas Shutdown. Here is what you can do:

1. Check for fluctuating pump pressure (air in strainer, pressure guage bounce)
2. Check all wiring connections
3. Replace ignitor/flame sensor assembly

Depending on your expertise, it could also be the gas valve or ignition control (aka the IID).

Since the burners do fire briefly, I would suspect the flame sense rod first. Attached is a link to the owners manual in PDF.

Lo Nox heaters can be a little tough so follow the directions exactly.

check breakers check power to trans former if 240 or 110 check for 24 v at the transformer if not volt, change transformer

Sounds like a problem with the thermal bypass or high limit system.
what is the model?

This happened to me and the tech came out and change the pressure switch and it worked fine afterwards