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

Can you describe just what the unit is doing when you say it just keeps running, does the fire come on and go off and the blower keep running or something else.

Tell us more about it.

More, more tell us more,yes thank you very much

Try this: disconnect thermostat wires from unit. If problem stops, inspect low voltage wiring for damage. Keep an eye out for suspicious-looking rodents loitering about.