I just tried putting in a single branch gravity recirculation loop and am running into a really strange problem. I've got a bottom feed hot water tank (ie: the cold water enters at the bottom), and the hot water exits at the top.
My incoming cold water supply is 1" PEX and my outgoing hot water is 1" PEX. The 1" PEX is branched off to 3/4" PEX which is connected to 1/2" copper to my kitchen sink. I tee'ed into the 1/2" copper and ran a 1/2" pex back to the HW tank. At the tank, I removed the original drain faucet and put in a Tee and connected the return line to that point.
So here is the weird problem. When I first put this config together, everything "seemed" to work better. I was getting hot water at the kitchen sink within 3-5 seconds vs. the original 40+ secs. However, I soon noticed that the hot water coming out of the faucet wasn't as hot as it should have been. I figured that I was having a problem with reverse flow; that I was getting cool water going up the return line and making the hot water at the faucet less hot. So I added in a check valve on the return line, figuring that would prohibit any cool/cold water from travelliing back up that path.
However, now the recirc loop doesn't seem to work at all. I'm back to waiting 40secs to get hot water from the faucet.
I'm really confused at this point as to why it seemed to work without the check valve and fails with it.
I know that a recirc pump would resolve the situation, but am trying to figure out why it would seem to work better without the check valve than with it.
I've used a SharkBite check valve, if it makes any difference.
Thanks for any insights!