Why wont an older model carrier gas furnace light when standing pilot light is lit at all times? Why would there be no gas at the burners

If your furnace is older than 1978 it has a standing pilot, which means it exists full time and is not intermittent in operation requiring a spark or hot surface ignition to ignite the pilot or pilot rail leading to the main burners.
If you depress the pilot valve button and light the pilot and hold it in for a minute maybe 2 and it drops out, the thermocouple is usually why. The thermocouple creates 30 millivolts of electricity, this is not very much power a millivolt is 1/1000th of one volt.
The 30 mv power is enough to hold the pilot valve open after you release the button after lighting the pilot, the replacement of the thermocouple is easy and they are available at any hardware store, they come in varying lengths, it is better to get one a bit longer than not long enough, you can loop the remainder.

pilot lit on gas furnace, but the burners won't light (Home ...

answers.angieslist.com > Home > HVAC

Oct 26, 2013 - i have a gas furnace with a lit pilot, but the burners won't light. ... I hv gas furnace we turn thermosate on upstairs but still wont turn on coud turn ...

Furnace Not Starting - Clean the Flame Sensor - YouTube

? 3:15
https://www.youtube.com/watch?v=Ecd5CzJjss4
Jan 4, 2012 - Uploaded by Home Improvement Videos
If you woke up to find that your gas furnace is not starting or it's ... If this sensor gets dirty (and they almost always do over time) then your furnace will try to light, ... working, you can hear it starting, but the burners on not coming on. ... The furnace nowcomes on every time and the house is nice and cozy.

Furnace wont start. What to do before calling the repair man ...

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https://www.youtube.com/watch?v=yJxDc90hs4g
Sep 12, 2012 - Uploaded by grayfurnaceman
Our property manager is great about sending a repairman, but the house is a mess. ... While troubleshooting my downstairs furnacethat wouldn't turn on, I turned off the ... Not sure what to do now about flame rollout switch..

pilot lit on gas furnace, but the burners won't light (Home ...

answers.angieslist.com > Home > HVAC

Oct 26, 2013 - i have a gas furnace with a lit pilot, but the burners won't light. ... if the thermocouple does not sense the heat of the pilot it prevents the gas controller fromturning on the burners. ... clamped onto the outgoing hot water pipe, if huydronic system) that is telling the furnace it is too hot, whether or not that is true.

There is really not enough information here to go on. If this furnace has a thermocoupling, the pilot will need to be lit manually. Follow the manufacturers lighting instructions carefully. If it still will not light you may have a dirty pilot assembly or a defective gas valve. Modern furnaces do not use a thermocoupling. There is no standing pilot light. Each time the furnace needs to be lit it will be done electronically. Many reasons why it wont light in this case. Safety control could be preventing it from lighting for safety reasons. A bad ignitor, ignition module, circuit board, gas valve, pressure switch, gas supply, induced draft motor, blocked or restricted flue pipe, cracked heat exchanger, dirty flame sensor, ect. ect. ect.

Good afternoon Victor. It is a good sign that your pilot light is staying on. That means that the gas valve is recognizing the open flam and is keeping the pilot valve open. Now onto your issue. Can you tell me if the unit is a standing pilot or intermittent pilot(doe the pilot stay on all the time or is it lit with a spark upon a call for heat)?

Troubleshoot an ignition problem on a Lennox gas furnace ...

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https://www.youtube.com/watch?v=yXIxgzwMkPs
Nov 17, 2012 - Uploaded by grayfurnaceman
This furnace should light its pilot with a spark then the pilot proves its on ... Troubleshoot an ignition problem on a Lennox gasfurnace .... Pilot and no inducer but is the same model as that great video! ... You probably have dirty burners. ... How do you know spark module is not sending 24 volts to mv and pv ...

Lennox Furnace Model G11Q3-82-2 - RepairClinic.com

Thats a safety.

The unit senses a failure to ignite, so it goes into safety mode keeping the blower running to prevent overheating and fires. And keeping the inducer motor running to prevent the same, as well as raw gas build up inside the unit.

The newer systems are "smarter" and can detect more specific problems and failures. The older ones simply know that the thing didn't light, so they bring on the fans for safety.

unless you are well trained in troubleshooting you need a pro .carrier furnastys are overly complex you should call carrier dealer if you want the shortest route to a workin system

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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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