Lisle 24780 Spill Free Funnel, 18 Pc.

A tale as old as time... Most common failure on our cars. You don't want another OEM unit as they are plastic and the coolant damages them over time. Buy one of these today (they are in stock at Home Depot, Lowes, Walmart, Autozone, etc.) and replace: https://www.oreillyauto.com/detail/c/dorman-help/dorman-help-straight-heater-hose-connector/mtm0/56430 Make sure you top off the coolant: https://conceptzperformance.com/nissan-infiniti-nissan-oem-blue-long-life-engine-5050-prediluted-antifreeze-coolant-999mp-l25500p-universal_p_14339.php and bleed the air using one of these: https://www.amazon.com/dp/B089T73TGJ

Have you scanned it to see if there are any codes? Do that first and see if it's a sensor issue. Who installed the water pump? How did they go about filling the coolant? Since it presumably has fresh coolant in it, I would try one of those elevated coolant funnels that screws on to the reservoir cap. https://a.co/d/02fIhYLN. You can fill it with coolant much higher than the reservoir to force air out of the system. Hook it up, fill it up, start car, heater on high fan on low, let the car heat up and see if you get any major bubbles out. If that doesn't work I would try doing a proper vacuum bleed. Drain all of the coolant and start over. You'll need access to a decent size air compressor. https://a.co/d/00adpZ2o. This is the fool proof way to make sure there is zero air in the system.