Teledyne laars model #LLD400N nat gas input 999,000 btu"s everything fires up...just no heat.

SOURCE: Where can I download an instruction manual for

You can download some information from;
http://www.manatron.net/Pdf's/JANDY%20MANUALS/heaters.pdf

This will give a parts list, applications and diagram.

SOURCE: Teledyne Laar 400k btu heater heater fires but wil not stay on

The most likely cause is a defective limit switch on the header. There are two limit switches, a "high limit" and a "low limit". They are mounted in wells next to brass plugs in the thermoplastic header just below where the water outlet is. They have shiny metal covers over them and you can see the wires going into the wells just below each cover. With time and use the brass plugs begin to seep pool water, corroding the sensors. If the sensors are open circuited the ignition controller will not allow the hot surface ignitor to fire the gas. Even though this is a failure of the limit switch it will show up on the diagnostic panel as "AGS" (automatic gas shutdown) because it is not a temperature limit problem but an "ignition problem."

SOURCE: starting a teledyne laars heater

check for proper millivolt reading( 400-600).it could be 20 different problems and/or components

SOURCE: My teledyne laars pool heater will not cycle on. The pilot is lit and the valave is in the on position

check millivolt output should be 400-600.if less than that you dont have enough voltage to power valve

SOURCE: Convert Laars lite model lg125n to LP gas

i dont have a solution, but i would like to do the exact opposite. I would like to convert a lg125 from lp to natural gas. have you learned anything?