Recirculation systems need a cross-connection between the cold and hot water so the pumped water has a way to return to the water heater, without this the pumped hot water won't flow! Grundfos does this via a 'thermostatically controlled comfort valve' at the farthest point from the water heater. Your issue may simply be that this valve was under the kitchen sink and was disposed of when the old kitchen was taken apart. Below is an example of this Grundfos valve. It looks rather pricey but IMO there is little there to justify the price. Perhaps you can shop around and find them cheaper. The H and C water is plumbed into the ends of the valve (they are labelled) and the top outlets go to the faucet. As the recirculator pumps, water can flow from the H to the C side until the water gets hot and closes the internal valve.

https://www.supplyhouse.com/Grundfos-595926-Comfort-Valve?gclid=CjwKCAiAt9z-BRBCEiwA_bWv-ApHm-Tvb7x9pshYG7W0odtKtDWpoOusF8GFUA4vnUiY7hLIk9dmyxoCRusQAvD_BwE

Thanks for the reply! I looked everywhere in the house and couldn't find this part. So, I would have to assume that when they performed the demolition of the kitchen that this part was removed and not saved. The kitchen isn't the furthest from the hot water heater and is on the bottom floor with the water heater. I would have assumed the valve would have been on the second floor diagonal to where the hot water heater was, but at the same time, I only have evidence of what is happening and that this part can't be found. Thanks for the suggestion and I will look into this part further.

Ok, so I installed the comfort valve in an upstairs bathroom and it seemed to help, but not fix the problem. It took 40 seconds for the water to turn warm, where as it was 8-10 seconds before. This was after the recirculator had been running for 15 minutes. Any suggestions for a next step?

Ok, I was able to get some info from the old owner of the house. As this was a new construction previously, it doesn't need a comfort valve. It has a hot water loop. In checking out the water lines under the kitchen sink, I'm seeing 2 unused lines. See picture below. The ones used are hot water, cold water to the faucet and then one line that goes to the dish washer. I think the dishwasher had an exit to one of the unused lines, but the dishwasher installer routed this to the garbage disposal. With a hot water loop, does anyone know how I would plumb the unused line?

With the typical description of a recirculating loop, what is under your kitchen sink doesn't make sense in that 'at the farthest point from the water heater, the hot water line is looped back to the water heater'. Issues with your under sink picture: 1} wrong location, not farthest from water heater, 2) too many pipes, only need 1 return pipe. This has a picture of a typical recirc loop:

https://www.nachi.org/hot-water-recirculation-systems.htm

Without some serious on-site investigation, I don't see how to sort this all out from a distance. Too bad you don't have an under sink pic from before the remodel. This is a long shot, but is there any way you could find THE original plumber for the house? They would have a much better basis to start from.

One thought on how a DIYer might investigate all this. What you need to know about those pipes under the sink is where do they each go so you can build a pictures of the plumbing design. If you shut off the water to the house and released the water pressure, one might be able to connect a compressed air line to each of those pipes in the kitchen and with judicious closing of some valves and opening of other valves elsewhere in the house listen to the compressed rushing though and determine where each lines go. Just a thought, and along shot at that.

BTW, kudos to your recent remodelers: that back wall in the cabinet pic is nicely done. With all those pipes there, that cabinet could have been totally butchered by some plumbers.

Thanks so much for the response. It's helpful. I was able to find some pictures of what the piping looks like behind this. I'm not sure if they are helpful or not. It sounds like I need to find out who did the plumbing on this house as it's getting a bit out of my depth.

Expanding your open-wall picture:

-The supply lines appear to be coming up from below.

- The two left supply lines are tied together. Because this piping continues on in two directions (and the middle two supplies don't), I am presuming that these are the cold water supply lines (sink & filtered water?) that then extends on to a possible toilet, outside faucet, or other cold water appliances elsewhere.

- The two middle supply lines are also tied together. I presume these are the hot water supply lines (sink & dishwasher?)

- The fifth pipe, to the far right, may be related to your return water loop described by the previous homeowner.

Ok, thanks for the help. I'll keep researching.