When lighting my LG model furnace the pilot will light but when I turn the gas knob to ON after holding in the pilot position for the minute it goes out and will not stay lit. What parts do I need to replace?

Turn the gas supply valve to on, then hold down the knob and light the pilot, hold the knob down for about 3 minutes to heat gas valve thermocouple so the pilot will stay lighted, it should then light off. If this fails the gas valve may be defective, they are cheap top replace.

Most instruction are similar but read How to light pilot carefully.
Did you apply a flame to the thermocouple until you could have pilot light lite?
most will have you hold flame for a couple minutes then rotate knob to on from pilot position.
remember be careful with gas and if still issue call plumber.

Well if you held the pilot knob down for 1 to 2 minutes before you turned it to on and it went out your thermocoupler is no good and needs replaced

see this causes and fix it. God bless you
o light the pilot on a standing-pilot (always on) ignition system, follow the lighting instructions located near the control. Otherwise, try these steps: Light the pilot:

1. Press and hold the pilot control knob to start the pilot. Set the control knob to the pilot position. Hold a long match under the pilot gas port.
2. Press the control knob; the pilot should light. Hold the control knob down until the flame is burning brightly (about 30 seconds). Release pressure on the knob, and turn it to the on position.
3. If the pilot goes out when you release the control knob, try relighting, holding the control knob down longer. If the pilot again goes out, check the thermocouple (below).

Adjust the pilot:

1. Remove any cap covering the pilot adjusting screw on a combination control.
2. Turn the adjusting screw counterclockwise to increase the flame or clockwise to decrease it. It is correctly adjusted when the flame envelops the thermocouple bulb by 1/2 inch and appears dark blue with a small yellow tip.

Test and replace a thermocouple:

1. Hold the control knob to pilot and light the pilot as above.
2. Unscrew the thermocouple fitting with an open-ended wrench.
3. Set a multimeter to the DVC (lowest voltage) scale.
4. Clip one multimeter lead to the end of the thermocouple tube nearest the pilot and the other lead to the fitting on the other end of the tube.
5. If the multimeter shows a reading besides zero, the thermocouple is functioning. Replace the thermocouple tube.
6. If there is no reading, you will need to clean or replace the thermocouple following steps 7 through 11.
7. Release the control knob and shut off the main gas valve on the gas-supply pipe that leads into the burner. Shut off power to the burner at the electrical service panel .
8. Remove the thermocouple from its mounting bracket.
9. Wipe the combination control clean and install a new thermocouple, tightening it by hand, then give it a one-quarter turn with a wrench.
10. Insert the thermocouple into the pilot bracket, being careful to not crimp the tubing.
11. Turn on power to the furnace and relight the pilot (above).

Adjust an adjustable burner air shutter:

1. Set the thermostat to its highest setting to keep the burner running. Once the furnace has heated up, remove the burner access panel and loosen the locking screw.
2. Open the shutter by turning it to the right until the blue base of the flame appears to lift slightly from the burner port surface. Then close the shutter until the flame reseats itself on the surface.

Clean removable burner tubes and ports:

1. Shut off gas and power to the furnace.
2. Unscrew or loosen and remove the tubes from the supporting bracket.
3. Carefully clean the tubes with a brush or vacuum, making sure not to damage the burner ports.
4. Use a stiff wire to clear any debris from clogged ports.

If this is a standing pilot system, turn the gas valve to pilot position. push in the knob & hold while lighting pilot...keeping holding knob down for a minute... this will pick & hold the gas valve. Let go of the knob & see if the pilot stays lit, if it does, then turn the knob to on position & the furnace should start if there is a call for heat from the thermostat

Hi, follow what I say and it is very easy. The knob that says off, on, and pilot, is where you need to start. You don't want to turn it off now, as its been off for awhile now. Turn the knob slowly pushing down on it until you fill it go down. The knob will go down believe me. When this happens, keep holding it down as this is what starts the gas to the pilot which is back under the burner, under it. Just take a flash light and you can follow the aluminum tubing back and where it stops is where you light it with something long with a match in it or a small rolled up paper. Keep the knob down the whole time you are lighting it. When it lights, keep the knob pushed down for about another minute. Then slowly release the knob and the pilot should stay on. Once you have it on, turn the knob to on, not off. If you turn it the wrong way, it will go off and you will need to start over again. Once it stays on by itself, turn your thermostat up for heat and the burner will light and come on. Just remember that the pilot where you light it is where the tubing goes back under it, as the pilot gas goes through it. You will need a light. Look at the knob with a good light and it will tell you which way to turn it. In the pilot position, the knob will press down to let the pilot gas in, and you can reach back and light it. Then turn knob on. Pilot should stay light. Turn on thermostat and it will fire up. Let me know how it goes. You may have to try a couple of times.
Sincerely,
Shastalaker7
A/C, & Heating Contractor

Just to make sure you are trying to light the pilot, from the gas valve follow the small diameter pipe (1/8") to the pilot assembly. Where you should be placing your flame is above that point. Now with the gas valve knob turned to the Pilot marking, depress the know into the gas valve. Light the pilot. Check to see if it is lit and remain holding the knob in for 30 to 45 seconds. If the flame goes out as soon as you let out the knob, you will need to replace the thermocouple.

The steps involved can vary slightly depending on your furnace model and pilot valve type, so if possible try and find the instructions inside the furnace door cover or in the instruction manual. This is for a gas fired furnace, but applies to any gas-fueled appliance including water heater. Two of the most common types of pilot valve body assemblies either have a red reset button and a gas valve or no reset button and a valve knob that can be depressed. But whichever type you've got, if you have an older model furnace with a standing pilot (flame is lit all the time) then this is the basic procedure.

• Turn you thermostat to 80 degrees or to a setting that will demand heat. Make sure the thermostat is in "Heat" mode.
• Go to the furnace and find the pilot valve. The pilot valve body is a box shaped device into which the main gas line will run and is located near the gas burners. It will usually have a gas **** or valve knob that reads "On, "Pilot" and "Off." Locate this gas **** or knob.
• Turn the knob or gas **** to the "Off" position and wait about 3 minutes for any residual gas to clear away.
• Find the pilot. It's located near the gas burner tube assembly in the furnace.
• Get your match or lighter ready. Sometimes the pilot is hard to reach. If possible, try and use a long fireplace match when you light it. If you don't have a fireplace match then a butane BBQ grill lighter works well too. If you don't have that, then you can fasten a match to the end of a stick when you light the pilot

• If you have a pilot with a red Reset button, turn the gas valve from "Off," to "Pilot."
• If you have a pilot with no red button, turn the knob from "Off" to "Pilot."
• Place the lit match or ignited lighter tip at the pilot and depress and hold the button or depress the knob as appropriate. Depress the button or knob for about 30 seconds. This maintains gas flow to the pilot until the thermocouple gets hot enough to open the main gas valve.
• Once the pilot stays lit, slowly release the button or knob and turn the gas **** or knob from the "Pilot" position to the "On" position. This will ignite the burners and keep the flow of gas supplied as required for the burners as called for by the thermostat.
• If the burners fail to ignite then it may be because the thermocouple did not get hot enough to open the gas valve. Wait a few minutes and then repeat the above procedure. This time hold the red reset button or depress the knob for about 45-60 seconds.
• Once the main furnace burners ignite, adjust the thermostat to the desired setting.
• If you've followed the previous steps on lighting the pilot and it still does not light after, or will not stay lit, then you probably have a problem with the thermocouple or an adjustment needs to be made to the pilot. You'll need a furnace service technician to replace or repair these parts. You may find that the pilot lights, but it is an anemic looking flame. That's a different problem we'll look at in the next section.
  
• If the pilot lights but the flame is a weak yellow flame, it will not get hot enough to heat the thermocouple to its set point allowing the gas valve to open.
  A natural gas flame should be a bright blue with the tip of the flame having just a tinge of yellow. A propane flame should have a bluish green flame with a tinge of yellow at the tip. The flame should be strong enough to hit the thermocouple tip about 1/2 inch from the tip end. If the flame is weak or shaky looking, check to see that a breeze or draft is not blowing on it. Adjusting the Flame
  There is usually a small screw on the pilot valve body that will adjust the flame. You may have to refer to the manufacturer's instructions to find the screw. Turn the screw as needed to adjust the flame throw. Yellow Flame
  A yellow flame is caused by lack of air and incomplete combustion. It can be caused by a dirty pilot tube tip. Split Flame
  This is caused by dirt in the pilot tube. Take a needle or small nail and gently clean the tube. Flickering or Wavering Flame
  A flame that flickers is usually caused by a draft.
  

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First step turn the thermostat off. It is very important.
Next find the knob on top of the gas valve you will see writing on it turn it to pilot it could be in the off position so move it to pilot depress the knob where it goes down about one inch. Take a long lighter long match or something like that and hold at the pilot it will be back in the furnace by the front of the burners. Once the pilot lights hold the button for another 30 seconds. Release the knob now the pilot should be on and the next step is why you turned off the thermostat rotate the knob to on position. Go to the t-stat and turn on the heat.

many of the newer furnaces don't have a standing pilot. look to see if you have a gas valve with a knob on top that says off pilot and on. look to see if a tube the size of a pencil comes out of the valve and goes down by one of the burners, look to see if there is a little gold piece of metal tubing protruding down to the opening of the larger tube . that is where you place the match. i prefer to use a grill lighter. safer and positive flame. turn knob to off wait 5 minutes for any gas to disipate. be sure your incoming gas valves are all open . usually at the meter and one at the furnace. usually the handle is in line with the pipe when open. from the off position, turn the knob on the furnace gas valve to pilot position and push down on it as you turn. this lets gas flow to the pilot tube by the burner where you have you flame starter lit and waiting. once pilot lights hold down on button for 3 minutes or less. longer is better to be sure the thermocouple senses flame . then gently release the downward pressure and the pilot should stay lit and you gently turn knob to on. if pilot goes out you may have a bad thermocouple. be especially careful if its lp or propane as that gas does not disipate like natural gas and can virtually lay on the floor till ignited. also consider having the heat exchanger checked by a pro with a carbon monoxide detector. they do crack after a few years and can be deadly when they do. good luck