On Tue, 23 Dec 2014 03:26:00 -0800 (PST), wrote:

My oil heater starts but dont stay on & my green light keeps flashing. It's set to reach a certain temperature & once it below that temperature the heater is suppose to reach that set temperature but it starts up &goes out after a few seconds.

How many is a few? Time it, at least twice, and tell us how long it
takes to go out each time.

By oil heater, dp you mean a full-size furnace, that heats the whole
house or apartment?

There are a lot of things that can cause your problem.

When is the last time the furnace was serviced? The last time the
nozzle was changed. They don't last more than 2 years and should be
replaced every year. They are only 6 or 8 dollars on-line, inc.
shipping, but make sure you buy the one speiified on the name plate
inside your furnace. And be careful unscrewing that you don't hit and
brake the insultators. A smallish wrench is needed for the inside hex,
like a 6" crescent wrench.

Do you have a round door you can lift up? Get in the habit of using a
long screwdriver, so you won't burn yourself when it's hot, and lift up
the door before it starts. Do you see a flame or the light from a
flame coming from where the flame would be? (not just a little light
from a continous spark) Does the light last the same length of time as
the furnace stays on before it goes out. Please get back to us with
the answer to these questions, yes or no, and we'll give you more
advice.

Do you hear the roar of the fire before it goes off?

Or just the small sound of a spark? Well, the spark you probably can't
hear because the fan and oil pump make more noise that it does.

Does it just try again to start on its own or do you have to push the
red button?

About how old is the furnace?

You can see several wires connected to the control board (in the box
with the red button)? If your furnace is new enough to have a
cadmium light sensor, and only the very old ones don't, you can test the
sensor by disconnecting one of the wires to the control unit, Get back
to me.

You can also test the ignition transformer before you buy a new one.
Unscrew the bolt or whatever is holding it down on a side that does not
have a hinge. Then press the red button to reset it, wait 30 or 50 more
seconds until it tries to start up again, and whenever it tries to start
up again, test the transformer by laying a long screwdriver witha well
insultated handle (and you should touch only the handle--keep your hand
at least 3/4" from the metal shaft) .... Lay the screwdriver on one of
the big contacts that the transformer has and then get the end of the
screwdriver very close to the other one. You should see a contnouse
spark from the other one to the tip of the screwdriver. Pull t he
screwdriver gradually away from the other one and the spark should get
longer, at least a half inch. If it's 1/2 inch or even 1/4 the furnace
should worlk, but the transformer is marginal. Let us know the r esults
if you do the test.

The electrodes might not be adjusted correctly.

The insulators might be giving the spark an easier path than jumping the
gap that ignites the oil but the service men have only replaced my
insultators twice in 30 years, and that might been routine maintenance.
They never came when the furnace was not working. All those times I
fixed it myself.

If you have an oil filter, it might be clogged. It's the size of a
car's oil filter, somewhere on the line between the tank and the
furnace. I don't have one so there is no filter to clog, but aiui the
filter element should be replaced every year, at least every two. If
you replace the filter, you may have to bleed the oil line so many save
the filter for last.