Here's the story:
I have a 40gal gas water heater that is only 9 months old - it's a
Rheem Fury model 22V40F1.
Within the last few weeks it has been performing very poorly. We used
to take showers sequentially and never run out... now we run out after
the first and during the first the cold water must be turned down
every 3 minutes to maintain a constant warm/hot shower. The water from
the kitchen faucet used to be scalding (tons of steam rising like
crazy) and now it doesn't even break 115 degrees F. I have not
changed the setting on the thermostat since the beginning and it has
always been set a tick mark or two above the white mark (which
according ot Rheem the white mark is at 120.
I had the plumber who installed it come in to take a look but he
wasn't very helpful and passively brushed off my comments and
concerns. He basically said (after much prodding) it could be the
diptube or the check valve but that rarely happens so we wouldn't
check them. Well... enough about the plumber or I'd go off-topic.
I ended up calling Rheem to find what I could do and they gave me a
test that I was/am planning to take: 28 gallons of hot water should
come out within 10 degrees of the thermostat setting. Well, I went
down to the water heater to look it over just to get an idea of what I
needed to do for this test. While looking it over I noticed that the
copper tube that goes to the cold inlet of the water heater was warm/
hot (I'd say at around 105 degrees F). Any reason this should be?