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oil burner intermittent failure to light

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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

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