Author Topic: oil burner intermittent failure to light  (Read 7952 times)

Offline mechanicalhacker

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oil burner intermittent failure to light
« on: November 15, 2011, 10:41:33 AM »
Trying to troubleshoot an intermittent oil burner problem.  It's a Wayne burner in a Miller mobile home furnace, 25-30 years old with a Sundstrand pump, burning kerosene.

The burner starts up, but typically takes a long time (~30 seconds) to fire.  Once it does fire everything works fine.  Sometimes, however, it doesn't fire, times out, and shuts down.  When this happens it sometimes relights when the reset button is press, sometimes doesn't... and if it doesn't, it typically will work several hours later if reset.  When it's not lighting, there is spark (screwdriver across the contacts), and clean kerosene runs out if the bleeder is opened, so it's not water or other contamination in the system.

Usually it works for several days, then gives trouble, then works for several days again.

The nozzle (0.6gph, which I know has a tendency to clog, but that would't cause an intermittent thing like this?) and electrodes were just replaced.  Have disassembled and cleaned the pump.  This morning it wouldn't light.  I put a pressure gauge on the pump, it read 100 psi as it should... and the burner lit.  Going to monitor the gauge next time it fails, but does anybody have any ideas on where to look next?

Offline JWWebster

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Re: oil burner intermittent failure to light
« Reply #1 on: November 15, 2011, 10:47:31 AM »
Did they let the tank get low or use diesel fuel instead of Kero?
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Offline mechanicalhacker

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Re: oil burner intermittent failure to light
« Reply #2 on: November 15, 2011, 11:35:33 AM »
No, it's on scheduled delivery so it never gets low, and the red dye clearly identifies it as kero.

I might have suspected that it was draining back and the pump was losing its prime, but at the moment the tank is full, and the level in the tank is higher than the pump.

Offline Brent@CanBC

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Re: oil burner intermittent failure to light
« Reply #3 on: November 28, 2011, 01:29:08 AM »
When it fires up and the spray nozzle is working properly,  and the electrode is doing its thing,  if the flame "eye" doesn't see a flame to keep the circuted closed it will shut down, and need to be reset to make it fire up again.
 
 First off, I take a screw driver,  and while the transformer is flipped up and I fire it up, you should get a 3/4" spark from the spring contacts/or what ever style of contacts your oil furnace uses, to the screw driver, so that will eliminate that.
 
 Next probably is a dirty "nozzle" as if the spray pattern is not right, it will not reach the spark,  and no flame,  the "eye" will shut it off, till the "reset" is pressed.  Your pump couple could be also coming to its final life span, also     Brent@CanBC

Offline Brent@CanBC

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Re: oil burner intermittent failure to light
« Reply #4 on: November 28, 2011, 01:38:46 AM »
A filter was not mentioned.  Your pump pressure is good,  but if the "nozzle" doesn't have the right nozzle, or spray pattern, again, the eye will shut it down,  as it MUST maintain a flame.  The filter,  the coupler, the pump, and spray nozzle,  IF runing and working right,  will tell the "flame sensor" or "flame eye" to keep running, or stay closed.  Brent@CanBC

Offline Brent@CanBC

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Re: oil burner intermittent failure to light
« Reply #5 on: November 28, 2011, 01:50:40 AM »
Last but not least.   New electrodes were installed.   Not trying to piss you off.  Were they the right ones.  Was the right gap/distance apply'd?  If so,  the "nozzles" spray pattern must reach the spark,  and the pump/cuppler/filter must MAINTAIN its pressure, or again,  the flame scensor will shut it off.  Brent@CanBC

Offline Brent@CanBC

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Re: oil burner intermittent failure to light
« Reply #6 on: November 28, 2011, 01:54:13 AM »
Ok, this is the last post for now.   When you had the pump out,   if you took the shaft and try'd to move it up and down,  was there any play what so ever.   UP/DOWN, any play, REPLACE the pump.  Brent@CanBC

Offline mechanicalhacker

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Re: oil burner intermittent failure to light
« Reply #7 on: November 28, 2011, 05:31:06 AM »
After a few more failures, I verified that even when it doesn't light the pump is producing a steady 100 psi... so I checked the spark and it's more like 3/8" max.  Accordingly, I replaced the transformer, and it seems to be working fine.  It still doesn't fire immediately, but it hasn't failed to start yet.  Interestingly, the new transformer produces 20kW, not 10kW like the old one.  I will still recheck the electrode positioning eventually.

The old transformer, even though weak, makes a nice Jacob's Ladder... :)

Offline JWWebster

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Re: oil burner intermittent failure to light
« Reply #8 on: November 28, 2011, 10:17:51 AM »
This is very interesting. I have never seen an oil burner rig. Would love to see some photos.
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About the icons: The beer is tip link, if a tech saves ya some money buy em a 6 pack. The small green square=personal message. The green dot is a link to my web page on appliance repair and other general BS I love to post. The letter sends me email.
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Offline mechanicalhacker

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Re: oil burner intermittent failure to light
« Reply #9 on: November 28, 2011, 07:14:38 PM »


time lapse:


The sparks are orange because I wiped a salt water slurry onto the wires (sodium = yellow light).

 

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