I am pretty noob about it so I will try details at much as I can.
Name: Bradford White.
Model #: M450S6EN12
Serial no: SK3522723. Based on their web site, it was made in Oct 1998. Same year as the house was built (http://www.bradfordwhite.com/findaserial.asp
The control temp nob turns counter-clockwise (left to right - temp low to high). The more turn to the right, the redder (is it even a word?) the color becomes. The word HOT is about in half way.
I normally keep temp at HOT position. It's been fine since we moved in in Feb this year (cold/cool weather)
In April we have 2 hot days than normal weather (about 95 - 100). The water was not warm enough to take shower. Kept checking, only the pilot light, no burning. So I had to turned the control temp higher to get fire burning. After the hot weather gone 2 days later, I turned it back to HOT position. It's been fine since.
On the last few days, hot weather is coming back. Same problem is back too. Now, I have to turn the control temp pretty high in order to get the fire burning.
It's city water. Oh, I live in S.Cali - Inland Impire area.