Is there a 2 wire terminal that plugs into the thermocouple on your furnace? If there is, that is a safety circuit that is either loose in the fitting that screws into the gas valve, or the limits that are in series with the 2 wire off the thermocouple are tripping which will shut the pilot off much like if the thermocouple is not generating current. If no 2 wire thermocouple splitter, than it could be cracked heat exchanger, draft issues, not enough combustion air, delayed fire on startup which could snuff out the flame, or just a dirty pilot assembly (weak pilot).
Remove the cover over the burners so an inspection of the heat exchanger is a bit easier. Take an LED flashlight and a small telescoping mirror and inspect the heat exchangers front section above the burners giving special attention to the two sections of the chamber on either side of the pilot light. Many times there will be a hole in the chamber or a crack that will allow the blower that circulates the air into the duct blow out the pilot light.
If you are handy enough, consider turning off the gas and remove the ribbon burners prior to performing your inspection. The pilot assembly is probably attached to one of the burners. Lay them on the floor in the order in which they install in the furnace as some furnaces have dedicated left and right end burners and most older standing pilot furnaces have the one burner with the pilot mounting bracket.
To remove, many times you gently pull backwards towards the gas manifold while raising up on the front of the burners. Once elevated enough, the burner then slips off the brass spud (orifice) and forward and out.
The next reason the pilot can go out is because the safety 'holding' coil in the gas valve is defective. Its responsibility is to hold open electrically a safety circuit proving the pilot gas is burning so that main gas can flow. The thermocouple generates just enough electricity to hold the safety coil open. Coil bad = pilot out.
If your furnace is over 25 years old, there is a good chance there is a hole or crack.
Answers & Comments
Is there a 2 wire terminal that plugs into the thermocouple on your furnace? If there is, that is a safety circuit that is either loose in the fitting that screws into the gas valve, or the limits that are in series with the 2 wire off the thermocouple are tripping which will shut the pilot off much like if the thermocouple is not generating current.
If no 2 wire thermocouple splitter, than it could be cracked heat exchanger, draft issues, not enough combustion air, delayed fire on startup which could snuff out the flame, or just a dirty pilot assembly (weak pilot).
Remove the cover over the burners so an inspection of the heat exchanger is a bit easier. Take an LED flashlight and a small telescoping mirror and inspect the heat exchangers front section above the burners giving special attention to the two sections of the chamber on either side of the pilot light. Many times there will be a hole in the chamber or a crack that will allow the blower that circulates the air into the duct blow out the pilot light.
If you are handy enough, consider turning off the gas and remove the ribbon burners prior to performing your inspection. The pilot assembly is probably attached to one of the burners. Lay them on the floor in the order in which they install in the furnace as some furnaces have dedicated left and right end burners and most older standing pilot furnaces have the one burner with the pilot mounting bracket.
To remove, many times you gently pull backwards towards the gas manifold while raising up on the front of the burners. Once elevated enough, the burner then slips off the brass spud (orifice) and forward and out.
The next reason the pilot can go out is because the safety 'holding' coil in the gas valve is defective. Its responsibility is to hold open electrically a safety circuit proving the pilot gas is burning so that main gas can flow. The thermocouple generates just enough electricity to hold the safety coil open. Coil bad = pilot out.
If your furnace is over 25 years old, there is a good chance there is a hole or crack.