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Determined 01-09-2009 09:39 AM

Old Miller Oil Furnace
I have an old Miller oil furnace and whenever the points become dirty with carbon I clean them and also the nozzle. The model # is Moc 80. and it used to call for a .559 nozzle. Now I am told by the plumbing store that they have switched to a .579 nozzle in place of the .559.
Yesterday I called a repairman to come and check out the furnace because it shut off and it seemed like there was something wrong other than the points. He cleaned the points and reset them and changed the nozzle to a .579. Now it runs and gives good heat but the firing seems like it is not correct to me because I can now hear a rumble and sometimes it sounds like it skips and when the blower turns on it seems to run smoother.
I was wondering if the new .579 nozzle has anything to do with this or should i take it apart and clean and reset the points? I don't want to call the repairman out again because around they charge another service charge. (69.00)
Last January 08, after I cleaned the points and reset them the furnace ran very good and smooth. I could hardly hear the firing and it gave good heat until now.
Anyone have any thoughts on this? or some good advice?

(by the way if anyone is interested, i found that to clean the points and the nozzle, one should use Brake cleaner for it leaves no residue and does not harm anything because it evaporates)


beenthere 01-09-2009 03:19 PM

Might have a cracked heat exchanger.
Might just be the air is not adjusted right.
Might be the heat exchanger needs cleaned.

yuri 01-09-2009 05:54 PM

.579 is slightly larger than .559/ more gph so it will need more air and probably should be setup with a combustion analyzer. If it is in a mobile home go up on the roof and check the chimney/air inlet for blockage. Ditto what beenthere said.

Determined 01-13-2009 06:58 PM

Old Miller Furnace
Thanks guys for your help. My son said it is my imagination about the mis firing. Seems like the .579 nozzle puts out a stronger flame because we can hear it. The furnace works better now with the .579 nozzle. The pump shuts off at the same time as the motor and spark do. Previously it sometimes would spin beyond and leave a residue of oil in the combustion area. It has been a week now and all seems to be ok, so I am going to leave well enough alone. Spring is almost here. Then I am going to see if I can gather some funds together to pruchase a new heater.


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