The heater (Larrs lite 2) will not lights

Check for error codes and service manual on following link:
http://waterheatertimer.org/How-to-troubleshoot-gas-water-heater.html#intellivent

Replace gas control valve
http://waterheatertimer.org/How-to-replace-Honeywell-gas-control-valve.html

Gene:

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make sure it is a propane heater propane burns hotter than gas if not correct heater it will overheat if ok check gas pressure if not enough heater will overheat you also might have too small gas line and are emptying it

When you light the pilot lite you have to hold the button down until it gets the element hot enough to stay lit. If you hold down the button and lite the pilot and let it go right away it will go out. What to do is hold down the button and lite the pilot and continue to hold the buttn down for about 45 seconds to a minute then let it up very slowly and you will see if it is going to go out by the flame getting smaller as you let up on the button. If it does start to get smaller conitnue to hold it again for a few seconds and repeat the process of letting it up slowly. when the control element gets to the right temperature it will stay lit then turn your valve to "ON" and the fire will start up and continue to heat the water.

This is a problem with the thermo-pile. Yoiu need a 750 millivolt general replacement thermopile. You can purchase at your local HV AC supply store. Should cost about $45

you mean it is only staying on for 35 minutes, if this is the case, then readjust or replace thermal coupling, if bad it will not sense the flame or pilot light. it has to be in pilot light flame as to work properly. ( this is for a gas hot water heater). if bad it will shut gas off to heater.

if the ignitor is liting for the first 15 to 30 minutes and then it will not lite again you have bad gas coils,when they are failing they will work until they get hot then they shut down,the coils are located on top of the gas valve,take out the two phillips screws,remove the cover,change out one coil at a time,pull off the wire connector and install the new coils

It sounds like your main valve. The diaphram may be loose fitting or it has a small leak.

try removing and cleaning flame sensor with fine steel wool.its located in lower end of burner box,usually opposite side of ignitor

try cleaning the top of the pilot light jet if you can get to with small brush then blow it clean with a compressor.