furnace burner won't stay lit.


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Old 05-03-09, 07:21 PM
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furnace burner won't stay lit.

I have a gas fired furnace made by RUUD, 19 years old. At this point, the flame only stays on for about 20-30 seconds then shuts down and goes through the cycle of the ignitor glowing, the flame coming on and repeatedly shuts off after only 20-30 seconds. I replaced the filter, tried a new ignitor, the blower motor is working and the induction motor (fan?) by the vent pipe is working. It's getting warmer here in Jersey so I kind of stumbled upon this while working in the basement. I had noticed that the vent piping was rusted and had actually split in two sections so I replaced them and an elbow. After doing that, the flame only stayed on for 1-2 seconds. I then vacuumed all rust particles (quite a bit of them) and changed the filter. Saw somethig about limit switches but don't know how to test for that. I don't know what else to do, any suggestions? Call a pro? Thanks.
 
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Old 05-04-09, 06:47 AM
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I would look at the thermostat & the control board.
 
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Old 05-04-09, 08:01 PM
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Well it sounds like you have a flame rectification system. Try cleaning the "flame rod", found on the opposite end of the burners from the igniter. Simply wipe it off with a rag or steel wool.
 
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Old 05-05-09, 04:46 PM
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it doesn't have a "flame rod"
 
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Old 05-05-09, 05:15 PM
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Often when the flame sensor (can be built right into an ignitor system) is bad, then the flame goes out in about 4 seconds.

But often when the flame stays on longer, something is wrong with the drafting components of the furnace - which will include: the condensate water tubing and trap, the venting being plugged, plugged up vacuum port where 1/4 inch tubing plugs into the inducer motor, or the pressure switch itself.

If you have a 2 electrical wire pressure vacuum diaphram switch, you can jump the 2 wires together to see if it stays running then. If it does, do not leave that jumper on!! It is for your own safety. You must check out any of the possible causes I listed. We can help you with that, if need be. (If you have a 3- wire pressure switch, you would first have to let the furnace start, and when it gets going, then jump between NO and C, (which you will find printed on the pressure switch)

Ideally, you'd have a volt-ohm meter (mulitmeter) to test the 24 AC volt wires on the pressure switch with, and that would confirm to you if there was anything at all wrong with the furnace drafting components, as mentioned. I posted that jumper suggestion, in the event you do not own one. If you do own one, we can tell you how to use it and how to make the test. If not try connecting up the 2 wires togetherr as suggested, temporarily, for the test
 

Last edited by ecman51; 05-05-09 at 05:24 PM. Reason: added last paragraph
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Old 05-17-09, 12:58 PM
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I have a three wire switch. I used the jumper as you suggested, the flame stayed lit. I borrowed a volt meter but I'm not exactly sure how to do the check. If the meter reads 24 volts then it would be a drafting issue? If it does not read anything its the pressure switch? I have also replaced the draft inducer motor(fan?) as that was also very corroded and actually had a hole on the top. Can you please walk me through the test with the voltmeter? Thank You,
 
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Old 05-18-09, 06:02 AM
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Since you made the confirmation with the jumper, that automatically means you have power feed to the pressure switch and the pressure swictch is not letting current through it (without the jumper on, that is). Therefore you have to delve into possible causes of what makes a pressure switch not "close" electrically, on it's own. And you do not really need the voltmeter now.

Try these things:

Remove the soft rubber vacuum tubing that goes between the pressure switch and exhaust blower, at the blower end and ream out that nipple, as sometimes gunk clogs it there.

Make sure that rubber tube is on tight at each barbed end and has no cracks in it.

See if you have have water standing in any of the clear? condensate drain tubing. That is how your condensing high efficient furnace gets rid of the condensate water, - and with all condensing systems, a gook usually forms periodically to stop up that flow. (I have worked in commercial buildings where back ups of this has wrecked the walls and ceilings! But since I am good at working on wall repairs.....) The last furnace I had with your problem, that was my cause. What happens is the weight of the water in that tube pulls back on the pressure switch and does not allow the plunger of the diaghram to draw in and close the electric switch contacts in the pressure switch. Therefore, the entire condensate drain system must be blown out. Blow through the lines each direction -away from the furance towards and through the trap and drain(or condensate pump direction), and also back in toward the furnace. It should be all clear with little resistance. Often you will first feel water resistance and sounds indicitive of full or partial clogging. After you are through, you can actually add water back into the trap again as that keeps exhaust gases from entering the house and may assist the syphon action through that vented trap.

If it comes to this -Make sure outside venting to the furnace is good. That means if you have one or two pvc vents, make sure both are clear. How? Sometimes it is hard to tell if something is way in the pipe. So a good test to rule that out is to temporarily disconnect the pvc lines at the furnace and see if it runs then. If so, you have found what the problem is (clogged venting). But this is a real short temporary test that should not take longer than a minute to find out, due to carbon monoxide.

IF it is none of this stuff, then it is bound to be the pressure switch itself, but this is more rare. You have no way to test this without either a boughten or homemade manometer device. If you were interested, you can look up on the internet how to make one. However, you may not know what your pressure switch is rated to close the clontacts at. I think a ballpark figure though is about .9 inches of water column (point 9 -an extremely tiny suction). Me - if the other stuff does check out (I bet it don't though!) -then I just replace the pressure switch.
 
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Old 05-19-09, 05:34 PM
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I checked the drain tube, disconnected and blew through it and the funnel shaped end on the venting the tube was connected to, all clear. I'm not sure where the trap is you're talking about. I checked the tubing from fan to pressure switch, blew through that, check for cracks, checked to see if nipple at switch and inducer fan was clogged (stuck a thin wire down), all clear. I disconnected the metal venting, ran the furnace, no ignitor glow or flame. What I don't understand is this went from bad to worse after I replaced the induction fan. At least prior to that the ignitor would work and there was a temporary flame.
 
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Old 05-20-09, 04:36 PM
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I just reread your OP after thinking more about your METAL vent pipe and the rust. It is conceivable that condensate or rain water is running back down the flue into your exchanger and you may have a corroded exchanger with hole(s) in it. That be bad news if that is the case, and it could be very unsafe to use due to carbon monoxide risk.

Maybe you do not even have a condensing high effiecient furnace, and you just have powerventing. If your furnace condenses, you normally would have the PVC pipe and you would have a drain line going into a trap and then continuing on to a drain -or - a condensate drain hose that goes directly into a little pump mounted at the outside base of your furnace. Do you have either of these methods?

Can you rehook up the jumper again to get the furnace to go and then observe the burner flame and see if it jumps differently at all right when when the blower fan (that puts heat out the registers) comes on? Yo have to carefully stare at it during this sequence.

It be nice to see pics of your furnace, taken so we can see the venting and how it hooks to the furnace, and you could explain where the corrosion was and where you replaced the sections - and shots of the inside of the furnace.

It's also possible that if the flame does not jump, that you either have some issue with the drafting - like the vent motor is not quite right in say that there is a restrictor plate stuck in the rear of it that may not supposed to be there for your btu model, or the pressure switch is bad. But if the latter, you either chance it and buy one at your own risk (figuring that a furnace man's charges at showing up at your door may cost more), or try to do a manometer test to see if the suction through the pressure switch vacuum line is sufficient to pull on the plunger at the rating of your pressure switch.

But if you do end up having a furnace man come out, then you maybe would have been off waiting on buying a pressure switch on chance.

But let me know about if the burner flame suddenly dances when the blower comes on. That we have to know.
 
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Old 05-20-09, 06:43 PM
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I'm thinking it's a powerventing furnace, there's no little pump mounted anywhere and the clear drain line goes into a small white (1"?) horizontial pvc pipe that leads to the french drain and also back towards the a/c coil, but no trap. I did forget to mention that the metal venting is connected to "ultravent", light gray in color, that is directly vented outside through the back of the house, not through the chimmney flue. It doesn't seem to be clogged, I can feel the air coming out, similar to a clothes dryer vent. I used the jumper again and saw no flame jump. I also disconnected the rubber tube at the pressure switch to see if I coulfd feel any air coming out. Felt nothing substantial but sounded like air was coming out. I'll try a new pressure switch, if that doesn't solve the problem I'll call a furnace professional in. Don't want to injure myself or family. Thank you for all your troubleshooting advice. You have been a great help in attempting to educate me (you have). If you ever need some medical advice, maybe I can return the favor. Thanks again, cfpnorton@yahoo.com
 
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Old 05-21-09, 05:29 AM
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Before you replaced the vent pipe, the flame would stay on all the time? What is the model# of the furnace and the afue rating? Tell us more about the old vent pipe. Was it single wall or double wall? Many manufacturers have only one or two vent fans for their furnace lineup. They "tailor" the airflow for each model by using an orifice plate at the fan outlet.
 
 

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