furnace shuts off, need help
 

I am having a problem with my furnace shutting off, for no reason. It is an old mobile home Coleman kerosene/#2 heating oil furnace.

It has fuel, it's getting fuel, it has a fire in the box. It kicks on and the pump runs. If I open the inspection door it has fire as soon as the pump starts. It runs for about 20 sec. and the little box on top of the pump trips off and the red light comes on. That is what it does if it runs out of fuel, but I have plenty of fuel in the tank.

I have to keep resetting it, maybe two three or four times then it runs. It may run fine for hours, then for no reason it starts all over again. It's not a huge deal when I'm home to play with it, but I'm getting tired of coming home from work to find it tripped during the day and now it's 30 to 40 degrees in here.

Any idea how these things work or what could be wrong with it?

Thanks in advance.

I believe you have a malfunctioning stack control. Search google for oil furnace "how it works"

Some oil furnaces also have a photo cell that has to see the flame or it will shut the furnace down . Sometimes the photo cell will get soot on it & cause it to stop working or sometimes they go bad . Have you replaced the oil filter at the tank ?

I don't see anything that looks like a stack control. The only thing I see is this

http://www.honeywellparts.com/honeyw...r-control.html

I also don't see anything listed as a photo cell. The filter was changed last year. I don't have any problems with fuel getting to the burner as I have fire as soon as the pump starts.

Stack relays are getting to be pretty rare, but yeah it likely has a cad cell flame sensor and it does sound like that could be it. Turn off the power. Open up the transformer (it is likely on a hinge) there should be a little lense with yellow wires (likely) it may have soot or a film of some sort from dust sucked up by the burner fan. Clean the lense and try that. if that works you may be OK but I would get it serviced by a technician. Could be the nozzle or a weak spark too. Could be the dirt is in the blast tube requiring the drawer assembley to be pulled. Could be a worn pump drive or even the pump. How old is the furnace?

That's the primary control or primary relay. Could be the yellow flame sensor wires are loose on that control too. Worth a check. They're marked as F and F

The only electronic items on it and listed on the wiring diagram are as follows:

1. Upper limit switch
2. Lower limit switch
3. Fan switch
4. Ignition transformer
5. the Honeywell oil burner control in the above post
6. Blower motor
7. Pump
8. the master on off switch

Regardless an 8184 control needs a cad cell sensor. It's likely slid onto the base of the transformer inside the burner. Could be n the burner frame too, I don't know what burner you have.

Under the transformer I found a sensor of some sort. It was clean, but I took a rag to it just in case. Also there were two large copper contacts between the transformer and something inside. I sanded them down to clean copper, just to make sure of good contact.

No good. I turned it back on pump ran for a few seconds and shut off.


Edited to add: I made sure the wires marked F F were tight, as well as any other screw I seen.

Plugged nozzle most likely but there are a multitude of other things like the electrodes need adjusting, or they're cracked or the blast tube is dirty stopping the flame light getting to the sensor, or the bus bars are weakly attached (the copper contacts push against the bus bars or maybe you have electrode rods) or a very weak transformer (good chance of that too) Thing is you're getting into needing specialized tools to test things and and specialized knowledge to replace things. Probably time for a service call. Did you check the sensor connections to the control?

The photo cell is working. Took it out hooked it up to a DVOM sparked a lighter in front and got continuity.

Well that's not quite how you test it but its likely OK.

There are 3 or 4 holes in front of the photo sensor. I held a flashlight down in the fire box and could see the light through the holes. I took a rag and cleaned the outside as best I could and took a Q-tip and cleaned the holes out just for giggles.

Still no go. Pump kicks on, nice big fire in the fire box. Still shuts off after about 20 seconds.

It's been a few years since I worked on furnaces & it's amazing how much a person can forget but if I remember correctly you could put a jumper wire to the two connections the photo cell goes to & confirm whether or not the photo cell is working . If you do that don't leave it that way . From everything you're saying it always fires right up & goes out while burning . The only things I can think of that would do that is the photo cell , loss of fuel or the high limit switch . How dirty are your air filters . I have seen furnaces kick out on the high limit switch because the air filter was so dirty the fan couldn't pull enough air to cool the firebox . If anyone knows I'm wrong about jumping the photo cell jump in here & say so . I've also used a jumper wire to by-pass the high limit switch as a test . I never leave any jumpers in place after testing . By the way does the fan come on before the furnace shuts down ?

It has no filters. (edited: no air filters, it has a fuel filter changed last year) The pump kicks off before the fan comes on. I tried to jump the F & F contacts for the photo sensor and it would not do anything. Zip zero nothing. Hooked up the sensor again and back to the same thing.

It just seems strange that I can keep hitting the reset button as soon as it will reset and after a bunch of attempts it will work. I think it took 4 resets this time to get it to come on, it was starting to get to cool in here.

You said it took 4 resets before it would stay on . Did the fire light each time , burn for 20 seconds or so then go out ?

In a word, yes.

In an attempt to help diagnose the problem, I bypassed the high and low switches. Ran power directly to the pump, transformer, and controller, bypassing all the safety shut offs. Still same problem, runs then shuts off. So after that I'm going to say the switches are not part of the problem, and yes I hooked everything back up the way it was.

While this may not have been the safest or smartest thing to do, I did it anyway.

I unlocked the ignition transformer and let it rest on the contacts. This left about 1/4 inch of space under the transformer. I turned out all the lights and there seemed to be plenty of light coming from the fire box to the photo sensor. I just wanted to make sure there was light in the box to be seen.

I'm grasping at straws at this point:Bawling:

Can you bypass or remove the filter and see if it works?

I just now noticed that you're in WV too . I'm in Doddridge County now . I grew up in Upshur County & lived in Monroe County several years before I ended up here . At this point I have to think it's a fuel problem . I have seen fuel filter problems even though it had been replaced the previous fall . I opened one up & it had ice in it so obviously either water was in the fuel when delivered or somehow water got in the tank . If I was you I think my next step would be to check the fuel filter . Do you know when the nozzle on the end of the fuel line in the furnace was last replaced ?

OK when you jump the F terminals the relay is gettign a signal that there is already fire in the box, so it won't start as that could make things worse. So the primary relay is working reasonably well. That's why you got nothing when you jumped those terminals. It could still be the problem but that part works.
Here's what the tech should do first (so you know what you're up against)
Shut off the main power, and disconnect the fuel line from the pump to the drawer assembly. Hook up a pump pressure tester/shut off valve.
Reconnect the power and hit the reset with the fuel valve off. Check for the correct pressure. I'm going to guess an old furnace is running 100psi but there is a rating plate somewhere for the spec. of the owners manual.
If fuel presure is correct then the tech should test the transformer/ignitor (whichever) With the fuel still shut off (on the tester not the tank... that won't work well enough as you'll still get fuel from the line) the reset is set again and the transformer opened up, then with an insulated screwdriver they'll try to pull a spark from one contact at least a good 3/4 inch across. It's potentially putting out 10,000-16,000 volts so it's not for the faint of heart. Good spark there means pulling the drawer assembley. Once out the assembly can be checked for misalaigned cracked or burned off electrodes. Excessive carbon could allow arcing too. The blast tube can be cleaned and the f head checked. It could be rusted off and falling away. They should examine the combustion chamber to check its condition, if it has collapsed you won't get it to fire long. Everything good so far? Change the nozzle. It has to match spec. You can't swap a .65 80w with a .65 70 b it has to be right. reassemble everthing (if you changed the z position you really have to know where to reset it) and this time try to fire it with the pump tester valve open. If it runs you're on to test the relay for flame failure etc. and a combustion analysis.

I don't know; with the amount of fire I have in the box, I can't see how it could be fuel related. I'm not talking about a little fire, it burns out the top of the fire box almost to the bottom of the heat exchanger. It has yet to fail to start a fire, and a nice one at that. That said, if I have time after work tomorrow I'll stop at tractor supply and see if they have a filter for it.

As to the nozzle being replaced, I doubt it has ever been changed. I've been here almost 11 years now and I've never changed it.

I'm beginning to think the controller is going up. Just a guess, but I don't see much more in there that could be the problem.

Yup, I'm in WV as well. Grant county, we are on opposite sides of the state

If it still doesn't run it's likely the primary relay. You really can't do much without the pump pressure tester/valve. Or you could start a very big fire. It's time for profesional help.

I'd think of the transformer or the electrodes before the primary relay/controller myself. It could be the controler but they really are pretty reliable, whereas the transformers are not.

Is the primary relay that Honeywell controller? I'm not sure what you mean by primary relay.

yes its called the primary relay

Without testing and checkign everythign else it's a wild guess though. In my experience I would be surprised if that was the problem. Its almost always the nozzle or ignition.

That's kind of funny, I was looking at the transformer earlier tonight thinking it looked like it has been on there sense time began. The sticker on the front of it has turned yellow like very old paper does.

If I get a new transformer are they preset? Will I be able to bolt it on and be good or does it need some kind of tweaking?

First thing I'd do is replace the photo/cad cell & if the nozzle hasn't been replaced in 11 years it's way past due even if it isn't the problem . Sure doesn't sound to me like it's a transformer or electrode problem . If you happen to decide to replace the nozzle yourself the one that's in it now will have numbers & letters on it you can use to get one that's the same or it might tell on the furnace which one it takes .

ETA - If the transformer was the problem the furnace would have a problem lighting , going out after it lights doesn't sound like a transformer problem .

Well that is a basic wiring kinda thing, the seal has to fit exactly though. No tweaking. You can upgrade to an ignitor which runs higher voltage and a DC current rather than an old transformer ac. It could be the electrodes though and a new transformer might not change much or only for a short while, if the electrodes are the problem it could kill a new transformer over a short time.

Nozzle is a good start, just don't screw up the z adjustment.

If you want to properly test the cad cell use an ohm meter and see if it has less than 1600 ohms when in light.

That I can do. Give me a couple of min.

Photo sensor sitting on table 4 feet from lamp I get .299-.310 Ohms. If I put my finger over the sensor it goes to infinity. Lowest I could get was .038 Ohms a few inches from the bulb its self.

Playing with it a little in the shade, the highest reading I could get was 1999 Ohms then it goes to an open circuit.

Just a W.A.Guess here... Going back to the fuel possibility, is it possible to remove the nozzle, noting exactly the position, then let a couple of cups of fuel run through the pump into a jug and then inspect and replace the nozzle? If you had a scrap of debris that clogged the nozzle, then fell back, that might cause a problem like you describe.

I believe that the furnace is starving for fuel. I would take the supply line loose and verify that fuel is flowing from the main storage tank sufficiently to continue firing the furnace for more than 20 seconds.

I have no idea. Any guess is as good the next, I guess.

I just don't understand how it can run, warm up the place, shut off and then not want to work the next time. Reset,reset,reset,reset runs, warms up the place shuts off then again it won't work next time the thermostat calls for heat.

I have a feeling it's going to be a cold night.

The pressure tester would narrow the problem down and eliminate alot of guessing. And its safer. Funky partially clogged nozzles do act like that but so would a funky ignition. So would a host of other things I've already described and a couple of rarities I didn't. For every handful of cad cells and primaries I've replaced I've probably changed a truck load of ignition parts. Doesn't mean a thing in your case. Nozzles are cheap putting them in can be a little tricky. I really think you (we) need to stop guessing and hire this one out. if the guy follows a simple routine to test each component he'll find the problem quickly. Now transformers can fool you and so can multiple problems like an old nozzle and a dying transformer or a cracked electrode. You change the nozzle and the transfomer tests OK so you think your done. Nope the transformer weakens as it gets hot and it stops throwing a spark a day later you're back changing that too. You should get a furnace serviced annually but honestly if its really been 11 years you can expect a few problems now.