Can you clever folks tell me about this one? My husband did an
excellent job installing our tankless water heater. I was out of town
that weekend, but given his record for thoroughness, handiness with
tools, & researching how exactly to do something right, I believe he
put it all in right. It is this one right he http://www.ho****erheater.com/model-h-28-4.htm

However, now I can't get a hot shower!! I had nice long hot showers
with the tank system, but now, nope!! It starts off and builds up to
scalding water pretty quickly, if I crank it all the way up. Then I
push it back down to the correct temperature. But then it quickly
tapers off after a minute or two, and the rest of the shower is
lukewarm! It will get a little hotter & then colder in turns, which is
also annoying; but never gets hot, even if I push it all the way back
to the maximum. It's definitely not a comfortable showering
temperature, even.

Any ideas?