Shouldnt pose any problem, maybe some restricted flow due to the control valves design. Heater core is just like a radiator one line in and one line out, in between are multiple passages (cores). Think of it as a free backflush on the core! <img src="/forums/images/graemlins/kewl.gif" alt="" /> Seriously though, I would do a coolant drain, flush and refill with fresh coolant (unless fairly new). While system is drained, correct the heater hose connections and flush the core itself while apart. Garden hose is all it takes....and a catch bucket if you are in the garage.

~Darin <img src="/forums/images/graemlins/baby.gif" alt="" />