Bradford White gas water heater with Honeywell controls.

Going into the weekend, no issues - really hot water.
Sunday - no hot water. Check and 5 flashes followed by pause. Turned Off, reset, re-lit pilot. One flash indicating normal operation.

Thought it was fixed, but we are still not getting "hot" water. Burner lights, but water is not "hot". In other words, turn shower to full "hot" and it is acceptable to shower in, but not "hot".

Any ideas?

How old is the water heater? If it's pretty old, like getting near 8-10 years and never been serviced, it could be near the end of its life or need some major component replaced.

Is the bathroom shower the only place it's not getting fully hot?

When you re-lit the pilot light, you then turned the top knob to the "on" position. Did you turn level know back to the same setting it was on before? For instance, did you line up the arrow to the arrow instead of turning it to A, B, or C in the one below?

I have AO Smith water heaters with those damn Honeywell gas control valves, and I had the 5 flashes on one a about two years ago. 5 flashes usually means a bad sensor on the valve. I tried resetting and troubleshooting, but eventually just replaced the valve myself and it's been working fine since. I just got the 5 flashes on my second water heater so I'll be replacing the valve over the Christmas break.

From what I've read these are common issues with the Honeywell valves.

I researched it as well. Those Honeywell electronic controllers seem to be a problem across all the hot water heaters that use it.
I talked to the guy who installed it originally and he quit using the Honeywells because he was tired of having to work on them.
I had just about decided to change out the whole valve assembly for $200, but then thought about the fact the water heater was 11 or 12 years old and in the attic and decided to just replace the whole thing. I was probably influenced by my neighbor who was having to move out of his house since his water heater burst and they were having to remove all flooring and a good portion of the sheetrock.

The same guy who installed it 11 or 12 years ago put in a new heater with a mechanical controller like in the picture a couple posts up. He did it the same day I called him, but the price has doubled in those 10+ years.

He told me I could change the valve assembly myself as long as I drained the water out. His labor charge to change it was $200 (+$250 for the controller), but he said he has done enough of them he basically stabs it in under pressure, but would never recommend me doing it that way.

Thanks for the answers.