I have a Laars Lite 2. Pool an spa heater Model LD25ON. Nat. Gas It was working and then shut off. The pilot generator glows, but it never fires up. I have bypassed the pressure switch and still nothing. I did here clicking. I also by passed the thermo coupler also clicking but nothing fired up.

SOURCE: Laars lite II Pool and spa Heater LG model

Bad pilot generator? Flow issue?

SOURCE: I have a Laars Lite 2 400,000 btu pool heater. It

It could be that the Igniter has gone bad. Or it cold be a number of other items, like the gas valve itself. If the heater has a display panel on it, is there an error code showing? If there is, go to your Owner's Manual and find out what the code is for the heater.

If you do not have a manual, you can find one online at the following link:

http://www.inyopools.com/owners_manual/jandy_heaters_lite2.pdf

SOURCE: Millivolt pool heater will not ignite

Most heaters do not require power for the pilot to remain lit. Is there power at he unit? If it worked yesterday and not today has anyone turned it off at the circuit breaker? If you have power turn the gas valve off for 10 minuets and then relight to see if it needed a reset.

SOURCE: Laars LX400N with LCD display. Display not

You will probally need a new board but that is hard to say without being there. As far as the replacement goes;don't let all the wires fool ya. Each set of wires has a set number of pins it fits so not only is it difficult to get them wrong but when you put the new board in place the wires will have a memory to them and fall into the place where they hook up. Nothing to it, but get a book and be sure that you need the board first as they are pricey.Good luck

SOURCE: Teledyne Laars LD250 Propane Pool heater cycles on and back off

Do you replace the thermopile or check the milivolts?
Check the Pressure gas
You need replace all of them terminals and check again the milivolts at the gas valve