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This problem started with the first attempt starting the furnace this season. The furnace is rather old.

The pilot light is lit, and it works fine. However, when the heat call comes, the gas starts to flow for an instant, and then the pilot goes out. It is possible that the main burner also briefly (fraction of a second) lights before it all goes out.

The pilot light sensor was changed 3 years ago - it does seem to be sensing and working since the pilot light remains lit, and needs to be heated a bit before it stays on.

I also confirmed that the 24VAC solenoid in the valve is switching (outside of the system). However, I wasn't able to confirm that the valve was open outside the system - as it clearly needs more than just an electrical signal to open the valve. Unfortunately I didn't test it in the system by applying the 24VAC like I did outside. Guess I'll put it back in the system to see.

Ideas?

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    For natural gas stuff I like an expert to see it. Too many houses having rapid non expected deconstruction happening when stuff goes wrong. The main burner should not blow out the pilot light, but the flame sensor might be dirty, not seeing the flame, and turning off the gas. CO is also dangerous causing people to die in their sleep, so a CO detector is a must, if you want to see the morning.
    – crip659
    Commented Oct 29 at 22:15
  • @crip659, your options are noted, but doesn't help solve the problem. If I can not get the value work, I'll just have to bypass the value and turn the flow on and off manually.
    – pathfinder
    Commented Oct 30 at 15:42
  • "I'll just have to bypass the value and turn the flow on and off manually" > "rapid non expected deconstruction". Please don't fool around in that furnace like this. Your local rescue workers will not want to be picking up pieces of your kids off the lawn. Serious words because this is a serious deadly matter. If you don't immediately know what to do, and you need heat, get a qaulified repair person to fix it.
    – Triplefault
    Commented Oct 30 at 18:13
  • It was sarcasm - but actually it would work just fine. I grew up with a gas stove that has a manual on/off valve - not even a pilot! My grandmother would put a pressure cooker on that stove and then sometimes wonder off. Similar to the boiler situation with it's assorted relief valves. Turns out buying an electric gas valve requires a license. Guess I'll have to use an air valve then! Anyway, lets focus on solving the problem, as then my kids won't light a camp fire on the floor, freeze to death, or use those deadly space heaters that burn down all those apartment buildings.
    – pathfinder
    Commented Oct 30 at 19:31
  • Furnace uses VR8200a2116. Is it a standard feature of gas valves that partially opened solenoids would shut down both the burner and pilot?
    – pathfinder
    Commented Nov 3 at 14:29

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The furnace has a automated exhaust damper, such that when the vent is open, a lever switch closes allowing 24VAC to go to the gas valve (vr8200a2116) solenoid. The switch has become corroded limiting the voltage seen by the valve solenoid. Possibly the valve operates in such as way that a partially opened solenoid shuts down everything.

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