Can you tell me how pinpoint the problem that I have about the heating system?
All of sudden the system does not ignite and no gas coming through the valve.
I guess that igniter and valve controller might be the case.But I am not sure what part should be replaced.

Gas willnot come through the gas valve if the igniter isn`t working,can you check for power coming to the igniter, can you check igniter by takeing it out and look for burned spots sometimes you`ll see a white spot where its burned into,, be careful they are easly broken, I`m saying all this assuming you have a electronic igniter