Water heater won't light?

So the propane was accidentally run out, like all the way, on a Saturday, this remained this way, cold showers and all, until yesterday when it was filled around noon. Stove lights fine, water heater lights fine, and runs fine until about midnight, when the pilot went out.

I went to check on it, found the pilot out, it re lit easy, then I spun the dial to warm and pow, big, rich, afterfire type situation, which blew out the pilot. Now the pilot won't relight. Removed burner assembly, checked pilot, looked clear I could see light through it, put it back together, light pilot, it lights easy, good flame, figure I'll let it run on pilot for a while, come back, pilot out, won't light again.

What the hell is going on here? It's a 5 year old Richmond. Never gave any trouble until the gas ran out. Is a bad load of propane a thing? I thought maybe a regulator problem, but that would be apparent on the stove, right? I don't think it's a thermocouple issue, then it would light fine, just not stay lit on it's own.

Since it ran all the way out could there be regular air in the line that needs to purge before pure propane is back to the point of the pilot? No real idea here, just spitballing, sorry.

In reply to KyAllroad:

No way, the stove and water heater are the only propane appliances. Dinner was cooked on the stove, and the water heater cycled fine for at least 9 hours including one shower and some laundry I think.

Bad propane can be a thing. I deal with it frequently in LPG powered forklifts.

Since the stove is working fine, I doubt that's what you're dealing with. Can you remove the burner from the water heater and check for a clogged port or oriface? Maybe blow some air or carb cleaner back through it backwards? It could be possible that when the tank was running dry, some dregs got sucked up. IDK if residential LPG systems use filters or not, but on the forklifts, the filters don't catch the most problematic impurities, which is tar like residue that doesn't vaporize when the LPG goes from high pressure liquid to low pressure gas.

In reply to HappyAndy:

Yes I removed the burner assembly, it was a bit sooty but otherwise OK, main jet was clear, pilot jet was clear, I removed the line and shone a flashlight down it, blew airduster through both jets, then put it in and watched the pilot work perfectly and then die again a few minutes later and refuse to relight. I didn't see any strange residue beyond the soot, which is probably at least partially to blame on the unit backdrafting occasionally (taller flue is on the to do list).

No filters, flow is low enough something like this works fine, and is present on the water heater in question.

Check your vent piping. If for some reason you aren't getting fresh air to the burner and getting the combustion gases outside, the burner will turn off and shut down the pilot since most have a simple 02 sensor. Do you have a CO sensor/detector near the water heater?

In reply to RossD:

This is a cheap "dumb" heater, pulls air from the room, vents through a draft hood and out the wall. Which as mentioned isn't quite ideal at the moment (a semi recent discovery), but it hasn't been a problem before.

Off hand, I'd suspect your thermistor has bit the dust, or at least is not working correctly. That's the thing the pilot light heats up to hold the gas valve open. Normal clue that it's bad is the pilot light keeps shutting off.

Also called a thermocouple.

My water heater was doing exactly what yours is doing and the fix was a thermocouple.

A thermocouple would only explain the going out of the pilot, not the not lighting at all, right?

EDIT: Poked at it again, this time the pilot lit without hesitation, held down button the full minute like the instructions say, and poof the thing goes out around the minute mark and won't relight.

Found the problem, finally, NO AIR GETTING IN.

http://waterheatertimer.org/How-to-repair-Rheem-FVIR.html

The stupid Flammable Vapor Ignition Resistant (FVIR) system tripped at some point, I was wondering what the bracket in there was for. Debating bypass, seems to me if the past 50+ years of water heaters didn't blow the house up, this one shouldn't either.

Don't try the following at home, you'll surely die.

Pulled it apart again. Reached in there popped out the little bracket and picked up the ejected clip, vacuumed the bottom out, discovered that a #10x1" SS wood screw threaded into the hole in the clip a little is a perfect fit in place of the glass vial. Pop it in and it seems to be behaving now.