I have an A. O. Smith Power Shot Power House GPSH 50 water heater.

I noticed that I had no hot water. I found that the unit cycles off and on and then the vacation lit stays lit and the unit stays off.

It is a gas hot water heater but does not use a flame.

The unit is about 5 years old.

http://www.hotwater.com/lit/im/res_gas/185171-001.pdf

Here is a site that might give you the info that you are looking for.

Supposedly it is self diagnosing, notice at the bottom of this page is a diagrahm showing the different LED light sequenses.

I hope this helps.