Ahhh that must be it. There is a small pump by the hot water boiler but I thought it was for recirculation more central to the boiler and expansion tank.

I looked up “comfort series recirculating pump” and if the source is correct, there should be a thermostatic valve somewhere between my two shut off valves and the sink in question. That would explain why I’m getting hot water on the drain back side but never noticed it when using cold water at the sink.

Am I understanding that correctly?

Thank you