Gas sometime ignites, sometime does not. Gas smell when it does not light up.

Ignitor alway gets hot. Voltage at valve solenoids seems right. Coils replaced anyway, problem did not go away. When gas is running it seems to run until thermostat turns it off correctly.

I am ready to replace gas valve, assuming that they are opening up late, like they are sticky.

I am told this is not a common failure. Is there anything else to check? Igniter would not go on and off if radiant sensor was not working.

Is there any way to check the valve, to know that it is not working?