Gas won't fire on hot water heater

Hi all,

My hot water heater's been running fine with both the electric element and the gas, up until today when one of my propane tanks ran out of gas (I only had the one tank turned on for some reason and noticed I ran out while cooking on the stove...).

After turning on the other tank, I fired up the stove again to verify the gas was running. That worked fine and I went on my way...

Later though, as everyone was taking showers, I noticed I did not hear the telltale sound of the gas firing for the hot water tank. The water remained hot thanks to the electric element, but without a gas flame at work. Just to verify that the gas was fine, I switched the fridge over to propane without any problem.

I've seen posts about reset buttons and whatnot, but unfortunately am too clueless to know if a) those would apply in this situation, and b) where they're located exactly.

Any help would be greatly appreciated!

Thanks,
John