I have replaced circuit board,and smart valve on a heil dual pack heater and air condtioner unit, thermostat also new but my heater just keeps running i have to shut off breaker to unit to start and stop,had new circuit board tested and they say its working fine,anyone have any other ideas..model number is pac042k080b,the heater keeps burning and the fan keeps blowing ,i've had the thermostat wires tested and there all good the licensed repair person has replaced circuit board 3 times because he thought maybe it was a bad batch,on 3 rd one had it tested and it's fine ,tech support recommended replacing smart valve but the heater keeps burning and blowing,he's at a loss and has never seen anything like this problem

I would 1st double check the wire connections on the tstat,make sure no wires are maybe touching 2 post,,,,,,and also double check or even replace the tstat wires from tstat to furnace. this wouldn`t cost that much and you would be sure ,,,,assuming you are sure the wiring to the new board are absolutly on correct.
was the problem there before or after the tstat replacement?

i would 1st double check the wire connections on the tstat,make sure no wires are maybe touching 2 post,,,,,,and also double check or even replace the tstat wires from tstat to furnace. This wouldn`t cost that much and you would be sure ,,,,assuming you are sure the wiring to the new board are absolutly on correct.
Was the problem there before or after the tstat replacement?

it was there before i just purchased the house when i moved in the original circuit board was fryed so assumed that was the problem replaced that and the tstat was older version so i replaced it with a newer one heater would come on and go off just fine about a week later it would just continue too run heater and blower,so replaced the circuit board again after a couple days had same problem again,replaced circuit board again same problem had circuit board tested say its working properly dis connected all tstat wires to heater and the heater and blower keep running tech support said replace smart valve did that but still does the same thing,i have no clue what problem is i will replace tstat wires and see if that helps ...