Problem with oil furnace

[RiverDog]

I have a problem with an oil furnace ignighting. It doesn't always come on unless I push the reset button on the control. It may work for a few days without any problems. I have replaced the thermostat and the wiring to the furnace is good. What do I need to look at next? Calling a plumber isn't an option.

 

[Modeps]

Sounds like you've got a plugged oil sprayer or dirty eye... just call your oil company and have them service it.

 

[Paperdoc]

Two directions to follow to diagnosis / fix: no oil, or no spark. To start, you need to see what is happening when the oil burner tries to start and fails. There should be some way to open a small observation port and peek in. It will be totally dark in there. When the unit starts up, the pump/fan motor will start AND an electric ignition arc should start, also. In the dark the ignition spark should be quite visible, even if you can't see it directly. You might even hear the arcing. No spark, no ignition.

If you can verify that the ignition is sparking, then use a flashlight to peek inside. Can you see a fine mist of oil spraying? If you can, back away quickly. The worst danger is that the oil spray starts and the ignition arc is delayed a few seconds, then ignites a large cloud of oil vapor. Big Poof!

NO OIL
If you have no oil mist, start looking for plugged filters or nozzle. Most systems have at least two filters for dirt. One looks like a little metal pot (the size of a large measuring cup) in the line coming out of the bottom of the oil storage tank. There should be a shutoff valve before it, and a way to open it up. I probably has a fine metal screen basket inside, or maybe a replaceable filter cartridge. Clean or replace, then re-install and make sure no leaks.

Next part is harder, because you have to get inside (MAKE SURE THE FURNACE IS OFF!) That means turning off all electrical power AND shutting off the oil valve at the storage tank. Be prepared to wipe up a bit of spilled oil. You need to unscrew the oil spray nozzle from the end of the burner. Once you do, you will find a small second fine metal screen filter screwed into the back of the nozzle. It also needs cleaning and re-installation. Or, even better, take the whole nozzle to a furnace parts place and buy a new one of the same size. That would solve the third possible problem - a plugged nozzle tip.

NO SPARK
Over time the electrodes for the ignition arc get dirty and wear down to the point the gap is too big and the spark fails. Sometimes you can clean and reposition the electrode tips close to the spray nozzle so they work again. You also can check the wiring to the ignition transformer, and the connections from it to the electrodes.

Good luck. If this does not solve the problem, call a furnace service person.

 

[RiverDog]

Originally posted by: Paperdoc
Two directions to follow to diagnosis / fix: no oil, or no spark. To start, you need to see what is happening when the oil burner tries to start and fails. There should be some way to open a small observation port and peek in. It will be totally dark in there. When the unit starts up, the pump/fan motor will start AND an electric ignition arc should start, also. In the dark the ignition spark should be quite visible, even if you can't see it directly. You might even hear the arcing. No spark, no ignition.

If you can verify that the ignition is sparking, then use a flashlight to peek inside. Can you see a fine mist of oil spraying? If you can, back away quickly. The worst danger is that the oil spray starts and the ignition arc is delayed a few seconds, then ignites a large cloud of oil vapor. Big Poof!

NO OIL
If you have no oil mist, start looking for plugged filters or nozzle. Most systems have at least two filters for dirt. One looks like a little metal pot (the size of a large measuring cup) in the line coming out of the bottom of the oil storage tank. There should be a shutoff valve before it, and a way to open it up. I probably has a fine metal screen basket inside, or maybe a replaceable filter cartridge. Clean or replace, then re-install and make sure no leaks.

Next part is harder, because you have to get inside (MAKE SURE THE FURNACE IS OFF!) That means turning off all electrical power AND shutting off the oil valve at the storage tank. Be prepared to wipe up a bit of spilled oil. You need to unscrew the oil spray nozzle from the end of the burner. Once you do, you will find a small second fine metal screen filter screwed into the back of the nozzle. It also needs cleaning and re-installation. Or, even better, take the whole nozzle to a furnace parts place and buy a new one of the same size. That would solve the third possible problem - a plugged nozzle tip.

NO SPARK
Over time the electrodes for the ignition arc get dirty and wear down to the point the gap is too big and the spark fails. Sometimes you can clean and reposition the electrode tips close to the spray nozzle so they work again. You also can check the wiring to the ignition transformer, and the connections from it to the electrodes.

Good luck. If this does not solve the problem, call a furnace service person.

Thank you, this is the kind of details I needed. I was a plumber for about ten years but specialized in water pumps and wells. I never had a oil furnace before, only gas, so I never developed any skills with oil systems. I'll look at it this weekend. of course it's been working flawlessly for about three days now.

 

[Paperdoc]

Seems you have an intermittent problem. You say it fails, but will re-start after you push the Reset button, and then run for many days / weeks. I am guessing the button you mean is associated with the flue sensor system. (My experience is with an older conversion gun system installed in a previously coal-fired furnace.) One key control is a temperature sensor in the flue just outside the furnace. When a firing cycle starts up it starts a timer. If the flue gas temperature fails to rise enough within the preset time, the control presumes ignition failure and shuts the furnace down, tripping the reset system. It will not restart until the Reset button is pushed. But if the ignition system works then, no problem until the next time it fails.

In the systems I saw before, in addition to the flue sensor, there were high-temperature limit sensors in both the flue (in the same unit as above) and in the upper part of the furnace itself.