Water Heaters - Water heater not always hot

Good evening, all. We have a Bradford White 40 Gallon Gas Water Heater (MI403TGEN12). We've been experiencing a problem where one night we'll wake up and take showers and there's plenty of hot water and the next day there will be none or barely any. There's nothing in our home that runs while we're sleeping that would consume any hot water so this is really confusing us. Any suggestions as to what could be causing this to happen? Thanks for the help/advice in advance.

check to be sure the thermostat on the gas valve is set at a high point and that when you turn it way up you can hear the burner ignite, its possible that the dip tube on the inlet of the water heater may be damaged somehow causing the thermostat not to sense proper water temperature and turn the gas valve on.

The valve had settings "HOT, A, B, C, and VERY HOT" It was set on "HIGH" and when I switched it to "A" the burners came on. After they shut off, I turned the knob to "B" and they came on again. I never realized there were settings beyond HOT. Looking at the knob directly from the top makes it appear that HOT is the highest setting. I couldn't see the A, B, C, and VERY HOT until I actually looked around the corner of the heater. Thanks so much for the help.

no problem, see if that will do it, just make sure you check the faucet temperatures with a thermometer so you dont risk burning any hands especially little ones. usually 120 is a good median, most wont go over 140

Yep, that definitely appears to have done the trick. My wife was doing the dishes and yelled upstairs asking me what I did because the water is much more hot than usual. It's not scalding or anything but it's noticeably hotter. I would assume we have whatever temperature regulator is required by code these days to limit the maximum heat the water can be set to because our home is relatively new construction (2000). Thanks again for all the help. It is most appreciated.