Cusser
+1y
Lalu - can you get ANY flow at all through the heater core, even a small amount? If so, I'd try cleaning it in place, as it's a LOT of work to remove the heater core. First of all, don't use toilet bowl cleaners, most are hydrochloric acid (the label will usually state what it contains because disinfectants are EPA-registered products). Hydrochloric acid will also dissolve the metal core. Use phosphoric acid, citric acid in solution, or acetic acid (vinegar) and get it pumping through at the firewall, can set up in a continous loop using a cheap pump. As the clog dissolves, the flow should increase. Then rinse with clean water when you're done. Wear goggles.