I have a goodman heater. Replaced the board and heat sensor and it runs for 20 sec and turns off. Starts all over again and again. What can I do next.

Did you replace the flame sensor? Or at least clean it?

I replace the sensor and control board

I replace the sensor and control board

See how many blinks the board does after you cyclt the power on and off and restart the furnace. Blink scheduak should be listed on the furnace legend/diagram on the inside of the blower door.

If not see this sample