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Re: new furnace flame rollout
Have you checked the venting either on the side of the house or on the roof ? did you or the company who installed it go by the specs on how many elbows and length of the venting run ? It also sounds like you have some blockage somewhere, if your in a climate that has alot of snow or some type of freezing rain, your intake or exhaust could be plugged by ice or snow, if so, a quick solution for this is if you have a shop vac , take the tube and hook it up to the exhaust side of the vac, then place the vac tube into the 2" vent wrap a rag around that to make a better air seal, then turn the unit on, if ice is the problem it will blow it right out ! if this does not fix the problem, I would consult the company who installed it and have them come take a look, should be no charge if the system is new, hope this advise helped, please rate this and let us know how we did, thanks for your qquestion, mr.grzz
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You will need to replace the limit switch if it has stopped working. But if it is still working, it is protecting you against over temperature conditions and is part of a safety circuit. One the biggest causes for limit switches to open is the lack of air flow due to blocked coils, dirty filters or improperly operating fans. You should never operate a furnace with a safety circuit overridden.
You mentioned it started when jumpering a safety switch, if it is the flame rollout switch then most rollout switches have a reset button between the leads on the switch. Reset the switch is easy and should allow the furnace to restart. The rollout switch detects just that excess heat coming backward into the flame sword area. Some causes for this to occur is cracks in the heat exchanger, the induction fan deteriating so the flue gasses are not exhausted properly, or a blockage in the flue gas path. Blockage can be caused by excess rust buildup in the tubing, dirt dawber nests, and any number of other obstructions.
Any way you need a professional to determine the cause for the limit switch opening.
Hope this helps.
1. Thermostat calls for heat.
2. Draft inducer motor starts.
3. Pressure switch attached by a small plastic or rubber tube senses the negative pressure produced by the draft inducer and closes.
4. Draft inducer runs for 30 seconds to a minute before you hear a gas hissing sound. The ignitor did not glow, the flame sensor (a small metal probe about 1/8" in diameter, with a white porcelain base) does not sense the flame, so after 8 to 10 seconds the hissing sounds stops with no ignition of gas to heat your home. Your furnace shuts down and goes into a lock out condition until you turn your power switch back off and on again. Then the sequence starts all over again with no ignition of the gas.
Solution:You probably need to purchase and install a new ignitor. I would suggest that you inspect your ignitor closely for cracks.Make sure you do not touch the ignitor with your bare hands. If you do not visually see a crack, then you could have a furnace control board problem or a limit, rollout switch problem. Please see "limits, rollout switches & furnace control boards" further down on this page. The furnace's control board might not be supplying the voltage to the ignitor. If your furnace lights and the gas stays on for 8 to 10 seconds, then shuts right back off, then you need to clean your flame sensor with light sand paper or steel wool. You might need a new flame sensor, but most of the time they can be cleaned an will work well after cleaning.
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If you have a cracked heat exchanger this will cause the flames to rollout and trip this switch. Its meant to stop the furnace from running and putting carbon monoxide in your home. Watch the furnace as it tries to light if when the gas valve opens and flame is established it should go into the tubes heat the heat exchanger and then your main blower motor will come on. When your main blower comes on is usually when you see the flames rollout and trip that switch. If this happens you can either buy a heat exchanger or new furnace if its a older unit Obama still has that awesome tax credit til 12-31-2010.
Look around for some popped rollout switches on the furnace. Try to figure out why the safety would pop out. The safetys are set to pop in case of air restriction or flame rollout from rusted burners. some repair pix
You need to find the rollout switch and see if it has a manual reset button on it or not. There are 3 styles of rollout controls. One is a disc type that mounts behind the burner ends, there may be more that one,possibly one on each side of the burner tray. This style rollout is usually manual resetting. It most likely will be black or silver in color and usually is about the size of a penny in diameter and about 1/2" in thickness with 2 wires going into it and a red push type button in the middle. The next style is similar two the first as it is manual resetting also, but this rollout uses a small copper capillary tube that runs just behind the burner ends and is mounted to the burner tray. If you follow this tube it will lead you to the manual reset button which is most likely mounted below the burner tray. The last style rollout is what they call a fuseable link, this is mounted behind a burner end and looks like a resister used in electronics, it is about 3/4" long and about 3/16" in length and is silver in color. It is mounted in a porcelain mount. This style is not resettable it has to be replaced with one of the same temperature rating. You would need to go to a Carrier/Bryant dealer to get the right one. Either take it with you or bring the model and serial number of your furnace. The most important thing about rollouts is that there is a reason it opened up(went faulty). The reason they trip or open up is due to the burner flames are rolling back out of the burner box and getting the rollouts hot enough to trip or open up. This is telling you there is a serious issue with your furnace that needs to be found and repaired. There are a couple of things that is causing this. They are that your exhaust is not venting properly. Your exhaust venting could be restricted with whatever. You need to pull your venting off and look for restrictions all the way from your heater to the end of the chimney. The next thing it could be is that your heat exchanger is cracked enough to allow positve air pressure on the exhaust system when the indoor blower fan is running. You can check this out yourself by watching the burner flames when the indoor fan comes on. If the heat exchanger is cracked enough the burner flames will flutter or move back toward you when the indoor fan comes on causing the rollout to trip or open up. Most manufacturers have a 20 year warranty on the heat exchanger(parts only,you pay the labor cost). Depending on the age and condition of your furnace it may not pay to have the heat exchanger replaced. I hope I was able to steer you in the right direction!! Good luck!!
Sounds like two problems. Not enough combustion air or a defective high temperature limit switch. You enclosure may not be getting enough outside air to properly sustain combustion. If the unit has a rollout thermostat it may be defective and stopping everything.
sounds like your burners need to be cleaned, you will need to pull them out and clean the rust out of them. the rust builds up on top of the burners and when you gas valve opens and fills the burners full of gas you will have a roll out of flames. hope that helps.