A question for mechanics. (No heat)

[Dunerdr]

Alright, I’ll start off by saying this isn’t my every day driver, but a truck I’ve owned since 2013. It’s got 273k miles on it. I really just use it for bad weather, riding four wheelers and lumber yard trips.

Last year it stopped blowing hot air. Not uncommon. I changed an actuator and replaced a blendoor. Still no go. Paid a friend who’s a dodge tech at the local dealership to replace the heater core on the side, after flushing and cleaning the it without success. After 3-4 weeks of good heat it stops working again. I’m somewhat mechanically inclined and figure maybe some trash didn’t get flushed. Warranty the core at orielly and slip my friend a few bucks to do it aft hours again. He does a full flush this time, all new coolant, we don’t use the dealerships recovery machine. Heats working it’s all back on the up and up.

My brother in law borrowed the truck from January until may. Today I realized I once again don’t have heat. What’s my next strip? A radiator? Is the water pump coming apart (100k miles on it roughly)? The radiator isn’t plugged I don’t think..