When replacing a furnace gas valve, use a pipe wrench to unscrew the old gas valve from the furnace system, and the fasten the replacement control valve in place. Use gentle but firm hand movements when using the wrench so as not to bend or twist the furnace pipes.
Before replacing a furnace gas control valve, check that the replacement valve is the exact match of the old one to prevent potential leakages in the furnace system once the new valve is installed. Turn off the gas control knob, and then turn off the gas control valve. This prevents gas from leaking while replacing the control valve.
Use a pipe wrench to unscrew the valve, and use your hands to gently pry it out of the system. Use the pipe wrench to screw the replacement valve into place. Make sure the valve is tight enough so it does not leak once the gas is turned back on. Turn the gas flow system back on by turning on the gas control knob and then the gas control valve. Regulate the pressure of the gas, and then light the fireplace to check the condition of the flame. When the valve is installed properly, the flame produced is blue with a yellow light.