Please read I need help!

I just got a B2200 for my son. Here is the proplem I have been having a heating problem. So I replaced the water pump it was totaly gone, new termostat and juast replaced it again thinking the first was was bad. Flushed the heater core. Well after burping it over and over again I still have this problem.

1) I start the truck it warmes up
2) I have good heat
3) After driving some time the heater blows cold
4) Turn heat off for some time
5) I have heat back for a little time

Please Help!

Change the temp sensor

Did you use a Stant 195 F thermostat?

Did you purge ALL the air from the cooling system? This is tricky on these, may need to top off several times, or jack up the front and run a few minutes with the cap off, topping off. Have the heater on while you do this.

Thanks For the help. But I just got done fixing it. I used CLR on the heater core flushed it several times. Finaly got more flow- But in the end i put in a new heater core.