Armstrong Ultra 80 Oil Forced air furnace

I had an LUF80B84 installed about 5-6 years ago. I’ve had to replace the transformer 2 times already and it produces alot of soot, a tremendous amount. I heard a boom and the furnace stopped working about a month ago and the service company came out and said it needed a cleaning. It looked like it had not been cleaned in 5 years the guy said, but it was only a year and a half. He said it was probably a delayed ignition which is usually a bad transformer, but he did a cleaning and changed the nozzle, filter. The guy also said my stack was very soft and should be replaced soon. Since the furnace sounded good he thought the very dirty furnace might have caused the problem and to see what happens.

Well the very next night I heard an even bigger boom and the stack literally blew into 5 pieces. I had them come out again (different guy) and he said the same thing, it is usually a weak or bad transformer. So he changed it and replaced the stack. He changed the nozzle again to be sure. Everything seemed good for about 3 weeks, but now since friday my furnace reset button trips about 3 times a day since Friday, 3 days now.

I have been reading alot on the web and see a note about the A coil for the AC can get clogged with dust, etc and cause too little air flow. This causes the exchanger to get too hot and this can trip the reset. This could be the cause since my air filter was dirty about 6 months ago and I took it out and meant to buy a new one. Well I never did and we have alot of dust and spiders where I live.

The furnace seems to run for a few minutes then turns off for a couple of minutes then comes back on. It just seems to happen so often and yet the temperature in the house doesnt get up to the set temperature. I have read that if there is too much back pressure that the air flow rate goes down and may cause the temperature on the armstrong furnace to go outside the stated range. Go to pages 19 and 20 for LUF80B84/95D12R
If I leave the thermastat on AUTO, the furnace blower runs in low mode, i think, so the temperature may go outside the range on page 20 above. The reset button trips more often when I do that, so I have been leaving the FAN in ON mode for the higher flow pressure. The reset still trips, but not as often.

I’m gonna clean the A Coil tomorrow, but I was wondering if there is anything else I should consider. Thank you very much for any information.

:smiley: :smiley: :smiley: :smiley:

Has anyone done a Bacharach test on this thing yet?

If your stack blew up, your heat exchanger certainly suffered. Your chances of having a ruined heat exchanger at this point are almost certain.

Well, new problem now. Maybe it is my beckett burner itself tripping. The heat just stopped again and I pushed the reset button. I hear a buzzing sound for about 45 seconds then it stops and the furnace does not start at all. I feel the right side of the beckett burner, looks like a motor of some sort, and it feels warm, not really hot, but definately warm. I read somewhere that there is a thermal overload in there and it heats up and that is what causes the reset to trip. I guess I have to wait for it to cool off and try to reset again.

Could that still just be caused by the A coil blockage and it is heating up this thermal overload. Then needs to cool down and I just never realized it since the heat goes out when I’m not at home or it is just a while before I notice it, so the thermal overload has a chance to cool off.


No one did any kind of check, but the first guy did say that the stack was very flimsy. He showed me by squeezing it and it looked rippled and it was very soft. So the stack blowing up may have just been the very soft stack pipes, but I will get it checked out. Could that be causing the furnace to trip it’s reset? Thanks.

Okay, new information. I decided to get off my butt and git r dun like Jae said. I opened up the A coil compartment and looked at the fins, no dust in there. Thought that was weird, so I went around back of the furnace and took off all the screws to the back panel. Opened it and no dust in there as well. Hmmm. Decided to go look at the filter section (thought there was no filter there), I guess I had put one in there many months ago and forgot. It was filled with dust (maybe an 1/8th thick on all the pleats hills and valleys). Took it out and put everything back together.
Pushed the reset button and I still get the humming noise. Thought that was not right so i just tap, very lightly, the top of the new transformer and the furnace kicked right on. Could they have installed a faulty transformer? Yesterday i did open up the transformer compartment and lightly sanded the top of the electrodes to make sure they were clean. The springs on the transformer seem to be making good contact with the electrodes, I have to push the transformer down about 1/8-1/4" to turn the locking screws.
Thanks for your replies.

Any one have any comments/ideas for me on my 4/8/07 @ 10:06PM post? Thanks.

BTW, furnace has been working perfectly now, very quiet and not cycling like it was. As a matter of fact I can’t even hear it running most of the time now, from the living area that is. Of course if I go to the basement door I can hear it faintly.

Wow??? transformers don’t have reset buttons, don’t have springs, don’t have electrodes what you are describing sounds like a relay/contactor transformers just reduce voltage no moving parts. Humming noises are most common with relays and their holding coils that make or break a set or sets of points depending on (normally closed) (normally open) Wow sounds like you need some serious help

Ahhhhhhh I keep thinking about your furnace problem just to let you know can not troubleshoot over a phone line or the internet and I am not the sharpest pencil in the box on oil furnaces have not messed with them since 1970.
But I can tell you if the exhaust flue blew off you have a serious problem and just changing the flue pipe is not going to resolve the problem. It sounds like you are having a delayed ignition problem don’t know what kind of safeties your furnace has in relation to flame approval but I can tell you that the heating Tech’s that you are using need to be replaced

You stated that you checked the furnace A-coil for lint blockage and observed none. I question that based on this furnace being in the basement an is probally an up-flow which would mean that the air inlet to the coil is not viewable on a true style A-coil as the air enters the bottom of the A. Some A-coils have a removal plate that will allow viewing of the fins some do not which requires partially pulling the A-coil out of its box in order to see the bottom. If what this furnace has is what we call a slant coil these types are viewable on both sides of the coil by just removal of the front of the coil box.

If this furnace has not had a return air filter in place for months I can guarantee the coil is matted over with lint and needs to be cleaned.


You really should contact a tech with a lot of experience with oil fired furnaces.

As Charley has suggested, it would seem you indeed have a delayed ignition problem. Each time the burner tries to light a stream of atomized oil is being sprayed into the fire box. If it doesn’t light the oil soaks into the surrounding firebox material which is ususally porous.
Each time you reset the system it tries again and if it doesn’t light off the fuel oil accumulates in the firebox material. Eventually it lights and now you have excess fuel to feed the fire. When it gets hot enough if vaporizes and rumble and maybe boom happens. Continued reseting of the system without normal lighting just adds to the problem an the potential hazard. I urge you to contact a qualified and experienced tech and fully explain the history of the unit for everyone’s safety.

The humming is coming from this 3" square device (transformer) which steps up the voltage. I tapped it lightly and the furnace fired immediately. So I think it may be a faulty transformer and at $150 or so installed I don’t want to miss out on the warranty for it by waiting until next season and maybe happening again.

Thanks for the response Michael. I’m not sure if you read my first post on this thread. I did have a delayed ignition problem and that is why they replaced the transformer. The current reset problem seems to have been from my air filter being clogged and causing the furnace to cycle too often, tripping the thermal overload in the burner. It is working very well now and I just am wondering if the transformer that was installed is faulty since it was humming last night after I changed the clogged filter. When I tapped the transformer it turned on and has worked since.



Glad to hear it’s working well now.
Transformers do sometimes hum because of their construction. The wires in a transformer are often wound around metal plates that are “H” shaped and stacked together. this however should not affect operation. The tapping you mentioned may indicate a loose connection at the transformer’s primary or secondary winding connections. Or the spring loaded pins may not have been making good connection. when you tapped it it may have made a good enough connection to operate. Keep a close eye on it in anycase for safeties sake. You may still want to contact a good oil furnace tech to run it by him. We just want you to be safe.

Michael, Thanks again. I’m thinking that the springs were making good contact with the electrodes, so the hum was inside the transformer, so I should have them replace it just in case, under warranty.

I would call and discuss it with them. I can’t tell from here how loud it is or if it’s really anything to be concerned with. Let us know how it turns out.

Yes we were not communicating on the same page I was thinking step down transformer and yes there are step up transformers as well but in the case of stepping up to an igniter I alway referred to this as the igniter package just different terminology same meaning in the different areas of the country. No it should not be humming loudly I would recommend having it checked. As mike stated better safe than sorry. As an after thought I probally would not really consider what you are calling a transformer a true transformer as this ignitor does not use AC voltage as the ignition point I would want to call it a converter just my thoughts.

Thanks Charley. I call it a transformer because that is what they call it on the service receipt and when i look it up online, I see them known as Allason Transformers that step up from 110V to 10000V.

Stephen I am just picking at you 110-volts to 10000-volts if this was Alternating current (AC) I think maybe it would blow up the furnace and your home. Lets try stepping up from 110 volts A/C to 10000 volts DC which is converted to DC by your igniter package or transformer if you perfer. Good Luck. Stay safe.

Charley the step up transformer for the oil burner ignitor is 10,000 VAC and no it won’t blow up in the furnace. No DC units that I am aware of.

Well I told you I was not the sharpest pencil in the box on oil furnaces just can not imagine not being DC have to go back to the books Thanks