Martin C. wrote:
On Fri, 06 Apr 2012 08:04:45 -0700, Bob F wrote:

Trader4 was right that the water returning from the loop should go
into the cold water return at the top of the tank, although it could
tap into a "T" at the drain valve at the bottom of the tank.

Here is a picture of where the hot water taps INTO the tank:
http://picturepush.com/public/7970412

That would be where the loop warming water RETURNS to the tank.

Here is a picture of the hot water flow FROM the two upstairs
bathrooms: http://picturepush.com/public/7970410


Notice the tank is actually the second in a series of two tanks
hooked up in parallel. It appears cold water arrives from outside
into the right- most tank, which heats it up and then sends ALL the
water to the left- most tank which again heats it up (I guess).

Q: Do I have enough information now to describe how the system works
yet?

It would seem so. The two valves on the two return lines would be used to adjust
the relative flow through the two pipes. If you reduce the time the pump runs,
you might want to check that those valves are as open as they can be to still
get hot water to both sinks in a reasonable time. One may need to be closed more
to increase the water flow in the other pipe.

Your direction arrows (from the other post) do seem right. The normal water
plumbing goes to each bath. A return pipe from each bath allows the pump to draw
hot water to the baths and back to the tank.

Is the pump quieter just hanging like that?

Do you have a giant jacuzzi tub? If not, you might try shutting down the first
tank in the series, which should save you significant heating gas. You could
always turn it back on if you have a lot of guests, but unless you have a huge
family, you may not really need it.

Is there a check valve somewhere in the return lines? If not, you could have
funny water temps at faucets in some conditions due to backflow through the
return pipes.