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Phil, Mechanical Engineer
Category: HVAC
Satisfied Customers: 8435
Experience:  Retired HVAC/ Electrical & Boiler contractor. Industrial
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Reznor waste oil burner won't stay lit. I got a new car

Customer Question

Reznor waste oil burner won't stay lit. I got a new car cell, it still won't sense the flame. I'm at a loss now........if I take cad cell wires off and "jump" it, it will light and stay running.
Submitted: 1 year ago.
Category: HVAC
Expert:  Phil replied 1 year ago.


In this case either the new CAD cell is bad, or waste oil debris has built up and is blocking the line of sight to the burner flame........ or.... the flame safety relay printed circuit card is going bad.

You can test for that... the flame sensing relays close between 750 and zero ohms resistance.. most will close as soon as resistance drops below 750.

To test this buy several resistors, 1,000 ohms, 750 ohms, 500 ohms 200 ohms. and 100 ohms... fit those one at a time across the CAD cell wires with the CAD cell removed... and see how low you have to with the resistors before the flame safety relay allows the burner to stay on.

Let me know what you can discover, we can go from there without a time limit.

Expert:  Phil replied 1 year ago.

You could also use a variable potentiometer and adjust it to read these various resistances.

Radio shack will have the, so will any electronics supply store in your area. You will only need the smallest and least expensive of those.

Customer: replied 1 year ago.
the igniter was replaced, and this is "new" cad cell #2. If I move the cad cell and adjust it, it stays lit at times, but not always. Not sure what you're talking about when you say flame safety relay card
Expert:  Phil replied 1 year ago.

Hello, when something like this happens, we suspect that a brand new part, directly from the sealed box, could be bad... it happens in 5 or 10% of the cases.

The fact that you have to move the cad cell indicates a carbon deposit build up inside the burner head, that is blocking the CAD cells view of the can visually inspect for that.

Those are pictures of typical flame detection relays that the CAD cell is wired to... just follow the wire from the cad cell, it will terminate at the relay... it is a complex affair about 5" cube in size, with a red button on the top to reset it (do not reset more often than twice, you can flood the boiler with unburned fuel that way and create a fire hazard.)

Look that over, let me know what you can discover, and do the tests with the resisters on the CAD cell wires... if that is no part of your skill sets, tell me which direction you are from the center of the nearest city and will get you a short list of well rated oil burner specialists.

Customer: replied 1 year ago.
K the relay is what I called ignition box. Sorry to confuse you. I just replaced it, it's brand new, the burner compartment did have build up, I've cleaned it all out thou. Would the nozzle keep it from staying lit? I'm certain it's boiled down to the sensor not sensing the flame. Question for you, I'm assuming that jumping it to stay on would be regardless of how dirty it was since I bypassed the sensor. Or am I wrong on this?
Expert:  Phil replied 1 year ago.

Hello again.

Yes, if you jumper the cad cell to keep the burner pump running, it would not make any difference if the cad cell could not see the flame or not... however you loose the flame safety feature and put the house at risk of fire.

If you have flame, then the nozzle is not the problem, however you could also have a bad nozzle that is causing soot to build up inside the boiler and needs to be replaced... that however would have no effect on flame sensing, since it does not take much light at all to operate the CAD cell.

Customer: replied 1 year ago.
K, so if I have that cylinder clean as can be, brand new cad cell and brand new circuit relay card ( the box where the cad cell is plugged into) this thing SHOULD stay lit. Yes I understand the whole flame sensor "hazard" I would never jump it just to make it work. Which is why I'm trying to fix it correctly.
Expert:  Phil replied 1 year ago.

Hello again, I can't think of anything else that could be wrong, except that you might have gotten a bad CAD cell... you can test it with a flashlight, it should go up to between 10,000 and 20,000 ohms with the light on it, and drop close to zero ohms in the dark... they close below 600 or 700 ohms in most cases, so it is a very broad range device, not at all touchy.

The female side of the plug it connects to could be corroded or suffering a spotty connection.

You can also use a potentiometer to see where the flame protection relay is operating.

Stay in touch, we should be able to figure this out sooner or later.