there are several safeguards that will protect you. If the igniter fails to ignite the burner there is a flame sensor, and if that sensor doesn't sense the flame it will shut the gas off. Usually when they install a new part they use the proper sealant and when they are done they check to make sure there are no leaks.

The people who make gas furnaces would go out of business if their products weren't safe.

Not to worry. 😊

The repairman that was out 2 days ago told me about the sensor and other parts. A different repairman brought the part and installed it. Glad we had such mild weather, so the house didn't get very cold.

You've eased my mind and I'm glad to feel less anxious. Thank you

The whole point of that part is to only allow gas to move when it is heated. It has parts that move, so they eventually break into the off position. It did its job and kept them safe, it should be fine now.

to the flame, then? And flame/gas cancel each other out if one isn't working right?
The 1st repairman brought 2 troubleshooting devices in. The first one didn't pick up the problem, and after using the 2nd device, said that it was pretty definite that it was the valve. I think he said a solenoid was involved. He said sometimes you could tap on the valve to loosen it, but didn't want to try that. He shut the system down. Today, I stayed in the basement while he worked and heard the reassuring whoosh of gas lighting up.

My daughter thought it might be the capacitor, and remembering we've had them go out on furnace and a/c, hoped that was the problem, just because it was familiar

Thank you for adding information.