oil burner intermittent failure to light

[mechanicalhacker]

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?

[JWWebster]

Did they let the tank get low or use diesel fuel instead of Kero?

[mechanicalhacker]

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.

[Brent@CanBC]

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

[Brent@CanBC]

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

[Brent@CanBC]

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

[Brent@CanBC]

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

[mechanicalhacker]

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...

[JWWebster]

This is very interesting. I have never seen an oil burner rig. Would love to see some photos.

[mechanicalhacker]

time lapse:


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

[JWWebster]

That's nice hallerween stuff but show me an oil burner in use. LOL

[Brent@CanBC]

Well JW,  it is nice when you fix and make something work the way its supposed to work.  When you go make out the bill and collect and your driving down the road,  thats when working on oil furnaces shows its ugly face.   Its the "smell" JW,  you go for a tea and donut, you smell from working on them.  I smelled like that all winter.
 
 Am not doing any furnaces or hot water tanks etc,  to old and am to stiff in the bottom half, hips, legs etc.  So I have worked on a lot of them,  and the people are sure happy to have their furnace working right.   So knowing what to expect in the oil furnace work,   believe me JW,  you are much better off sticking with just the Major Appliance Repair stuff.  You can clean for ever,  the service vehicle, the tools, the back of the truck,  at home,  even washing doesn't take all the smell out of things.
 
  I have to admit, I did enjoy fixing and installing this stuff,  even though the smell was constant.  Brent@CanBC

[Brent@CanBC]

You say it doesn't fire imediately.   You can get 100 psi,  but "is it" constant, 100 psi.  The single stage pumps are common on this problem.   Is this a single or two stage pump.
 
 When you first call for heat and the furnace comes on,  the spark is there,  then starts up,  and oil is pumped to the nozzle.  Usually it takes just a few seconds for it to fire up and have flame and the burner remains on. 
 
 If its "hesitant" in a flame,  you are dealing probably with the pump, if the coupler is in good reliable shape.  The blower/fan shaft is attached to the "oil pump" with a coupler.  I have had these pumps show 100 psi,  but still were not feeding a constant flow to the nozzle.  I would remove  the line from the pump to the nozzle and start it up and see what that gauge was reading.
 
 You might also have to attach a "clamp on meter" to the fan motor and see what kind of amps you are getting at start up,  you should get5-6 amps and and after it fires up it should settle at 3 amps .  If there is any "up/down" movement in the motor shaff what so ever, replace the motor.   This is the motor attached to the oil pump.    Brent@CanBC

[Icehouse]

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.

Red dye is added to Disel for use as #2 oil. This was done because fuel oil #2 was cheaper than Disel and truckers were using it to save money. If the DOT inspected the trucks and there was no "Red Dye" they knew the truckers were avoiding paying additonal tax.

[mechanicalhacker]

Red dye is added to Disel for use as #2 oil. This was done because fuel oil #2 was cheaper than Disel and truckers were using it to save money. If the DOT inspected the trucks and there was no "Red Dye" they knew the truckers were avoiding paying additonal tax.

It's the other way around... Diesel fuel has no red dye; red dye is added to non-motor fuel, which is cheaper because highway tax isn't added.  If the DOT sees red fuel they know no tax has been paid.