Hot Tap Water...Faster

I installed a Bosch Aquastar tankless on demand unit 12+ yrs. ago. The instructions said to rebuild the valve unit every year! I have never rebuilt it, & it is still working like a
champ. The only downsides to this older mechanical design are these; when it is hot outside the adjustable burner can't be turned down quite enough, which leads to the next
issue, mixing too much cold water in a restrictive fixture kills the pressure drop-shutting the burner off in the middle of Your shower. If You're using a well or spring, this may
not be an issue, but public water w/storage towers are another matter. I simply learned to let the sink run a little hot water while I was showering, not much, but it works....
and it never ever runs out! I could wash all of My cars, do 10 loads of laundry, fill a pool with warm water, & then take a nice long Hollywood shower!