I previously had an under-the-sink recirculation pump located in my kitchen. It was working fine, despite being ~7 years old.
Then, our kitchen was remodeled. Very minor plumbing work was done, and - from the best I can tell - the water lines were moved by just a couple of inches, to accommodate the new cabinetry/counter top for the sink. This included a cold and two hots (one for the dishwasher).

After this work was completed, my recirculation pump no longer seemed to work. I chalked it up to being old and maybe drying out (?) during the month of non-use. I bought another one, but this time the kind with the pump located at the water heater, and a small thermally-sensitive valve located at the sink (and anywhere else as desired). It's the Watts brand.

Now, it also doesn't seem to work. At least not at the kitchen sink (longest run, of course!). I installed a second valve in our bathroom and it seems to work there (much shorter run). I've also tried installing two valves in parallel under the kitchen sink (per Watts troubleshooting instructions), with no luck.

Naturally, I'm now wondering if there was ever anything wrong with my first pump - and that the contractor may have somehow caused my setup to become "incompatible"? I'm obviously struggling to think of what that could be. Somehow the hot water pressure still can't overcome the cold pressure at the valve - shuffling water between the two lines - despite the pump's assistance?

Any ideas? I do recall the water pressure in our house seemingly increasing a little bit when they were done with plumbing (observable only in the shower).

Thanks for any help in my mystery!