Tried changing the board, still flashing code 45. Will changing the gas valve help ?

This is a control circuitry lockout code that means one of the following three: Flame Sensor failure, Gas Valve relay stuck open, and software check error. Turn the thermostat to off --> cut power to furnace for 2 minutes and then turn back on. Have your spouse turn the thermostat back on and observe the sequence of operation before the fault re-appears so you can post it back to us. Thank you.