You may want to run some water out of the bottom first and see if flushing does anything for you.
Fourteen years is getting up there. My last two gas water heaters died at 15 and 14.
I just repaced my last one with a tankless unit. I'm surprised that Bosch would need hot water to advance. Most of the time, the water will cool in the pipes anyway. And most people I know turn on the dishwasher without running hot water first, so the first fill is cold water. I "do" like to run hot at the sink first so that I do get hot water for the first fill.