Furnace transformer blowing out on me every year

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Old 08-02-11, 04:41 PM
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Furnace transformer blowing out on me every year

Hello,

I have a forced air furnace that is fueled by fuel oil. The transformer needs to be replaced every year. The plumbing and heating guy has no answers for me as to why this is happening every year. I live in a 1940's home and has old electrical wiring. I do not believe it is knob and tube, but I am uncertain as I have lathe and plaster walls and I have not yet taken a peak behind them. The wiring to the furnace has a black fabric like coat around it. Can anyone tell me if it could be that the electrical wiring is providing insufficient power to the furnace and that is what is causing the transformer to blow out on me? I have a breaker not fuses. Please let me know if I need to provide more information. Thank you.
 
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Old 08-02-11, 05:36 PM
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When you write "furnace transformer" are you referring to the control transformer, the one that changes the 120 volts supply to 24 volts for the thermostat operation or do you mean the ignition transformer for the oil burner?
 
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Old 08-02-11, 05:44 PM
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I don't know which transformer it is that breaks down. I just know that is costs me $200 every year to replace it.
 
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Old 08-02-11, 05:54 PM
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I have moved you to gas and oil furnaces. It is very unlikely it is the house wiring having low voltage. More likely something in the furnace. The pros will need to know the make and model of the furnace.
 
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Old 08-02-11, 06:03 PM
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If it helps, my electricity does go out on me for no reason sometimes for a few seconds and comes back on. It happens when there is not a lot of electricity being used. I will get the model of my furnace.
 
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Old 08-02-11, 06:24 PM
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My furnace is a Tempstar, style #: RNUO112AF, Model #: NUOD112DG03 867.741425, 115 volts, 60 Hz, 14.7 amps, min circuit capacity 15.3, max fuse size 15, input rating BTU/HR 140,000, Rate Gal/HR 1.00
 
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Old 08-02-11, 07:51 PM
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Here is a link to pictures of my transformer. The black box on top is what gets replaced every year.

https://picasaweb.google.com/serenit...LSz6Zfg1YWY3QE
 
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Old 08-02-11, 07:55 PM
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We would need to know which transformer it is. IF it is the low voltage transformer then you need to install an in-line fuse on the secondary side to keep the transformer from blowing so it will only blow the fuse. If it is the primary control than I would recommend a surge protector on the furnace circuit if you are having electricity failures often.
 
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Old 08-02-11, 09:25 PM
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That black box, which appears to be be rather scuffed up, is the ignition transformer for the oil burner. It sure doesn't look to be only a year old, more like ten or twenty years old.

Are you sure that your service person isn't scamming you? That transformer should last for many, many years and they have newer models that are supposed to be more reliable than that.

Now what could be a problem is if your service person doesn't properly clean and adjust the spark gap inside the burner every year when he/she does the annual service. An improper spark gap can be the cause of early failure of the ignition transformer. Something else that can lead to early failure is an ignition transformer that is not wired for interrupted ignition, it should be de-energized after a flame is established.

Hopefully Grady will check in soon, he is an expert with domestic oil burners.
 
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Old 08-04-11, 02:31 PM
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I don't know if my service person is scamming me or not. He takes the transformer with him to his shop, brings it back, and then charges me $200. It may be time to get a new person to service my furnace, however, I live in a rural area and my choices are limited.
 
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Old 08-04-11, 03:18 PM
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There is nothing that can be done to an ignition transformer but replacement. Taking it "to the shop" is a scam.
 
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Old 08-05-11, 11:15 AM
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A scam? How terrible. Can I order this transformer and install it myself? Could someone walk me through it? Like I said, I live in a rural area and my options are limited. I don't think I will be able to get help from surrounding towns as there was a flood in those areas, and I am sure they are backed up trying to service those people.
 
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Old 08-05-11, 11:46 AM
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You may not need a transformer. Hopefully one of the pros will be along soon to guide you in troubleshooting. If your only thinking it is bad because of what your current repair person said I would take that with a grain of salt. What problem(s) do you currently have? Details please.
 
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Old 08-05-11, 03:39 PM
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I have lived in my home for almost 5 years now, and my furnace has broke down on me every year. I have an illness that leaves me quite ill, especially in the winter time, so I would like to have a stable furnace. I have had service people in from 2 different companies to repair it, however, it continues to break down on me. The last guy said he didn't know why my transformer kept breaking down, and thought that it may be the old electrical wiring that is causing the transformer to break down. Now, I find his judgement questionable. I would like to know if it is possible for someone to walk me through the process of changing out the transformer as I do not know if I will be able to get anyone here to fix it for me. I appreciate everyone's input. Thank you so much! If it is not the transformer, then I have no idea what else it could be. The last service person here showed me the transformer and showed me that it did not have a very strong spark ( believe that is the term).
 
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Old 08-07-11, 05:26 PM
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It is highly unlikely that your house wiring is causing any problems with the ignition transformer. Quite honestly, I think there is nothing wrong with your ignition transformer BUT that it is wired for continuous ignition whenever the oil burner is firing. This will cause the spark gap in the burner assembly to erode fairly quickly and THIS could manifest itself by the burner not igniting during a call for heat.

Generally the "primary control" (the grey box immediately right of the ignition transformer) can be re-connected to the ignition transformer to give what is called an "interrupted ignition" which means the ignition only sparks long enough to light the oil flame and then the ignition is de-energized.

I hesitate to give you any detailed instruction because I know nothing of your skills and working on oil burners is not a good place to learn handyman skills. It is also all but impossible to properly "tune" an oil burner without prior skill and special instruments. I wish I could help you more.
 
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Old 08-08-11, 09:28 AM
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Well, thank you all for your advice. I guess I will have to continue to pay a con artist $200 until I can find someone else to come to my town.
 
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Old 08-08-11, 07:46 PM
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Ignition Transformer

Sorry for the slow response. I too feel you are being scammed.
To be sure the servicer is actually replacing the transformer, they all have a date code either printed or stamped on them. Peel off the paper tape on the top & look for a data plate. The date code is usually a four digit number such as 1704 or 0417 (seventeen week of 2004). That transformer doesn't even look like an exact replacement but a "universal" adapted to your base plate.
That transformer is of the iron core type which VERY few servicers use today. Nearly all use electronic ignition transformers which are much smaller & produce a stronger spark.
 
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Old 08-09-11, 08:09 AM
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I really appreciate the advice. Thank you! Can you tell me approximately how much a new transformer would cost? Thank you for telling me how to tell the age of a transformer.
 
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Old 08-09-11, 09:43 AM
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Somewhere between $35 and $120 dollars depending on the exact mounting you need and whether you get the old-style magnetic or the new-style electronic.

Ignition transformers

Maybe you can call Patriot with the model numbers from your oil burner and they can recommend which transformers will fit.

I do want to caution you, I do NOT think the ignition transformer is the problem but is a symptom of the real problem. If you do not fix the underlying problem then merely installing a new transformer will fix nothing.
 
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Old 08-10-11, 11:24 AM
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Thanks again everyone for your advice.
 
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Old 08-10-11, 05:26 PM
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Transformer numbers

I'll save you the trouble of calling Patriot. That burner is a Wayne model M, MH, or MSR & these transformers will be an exact replacement: Sid Harvey T93 or an Allanson 2721-619. These electronic ones will also fit perfectly: Sid Harvey T93E, Beckett 51825U, & Carlin 41000-SO-WA3.
 
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Old 08-11-11, 04:15 PM
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You guys are sweethearts! Thank you!
 
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