Ruud Silhouette 2 burner not staying lit

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  #1  
Old 10-16-19, 11:14 AM
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Smile Ruud Silhouette 2 burner not staying lit

Hello,

I'm new to this forum and this is my first post. I've done quite a bit of reading on this forum and others trying to find and answer to my question but I haven't quite figured out the next step so hoping someone will be able to assist me. I'm quite a newb when it comes to HVAC in general but I'm armed with a multimeter, a few brain cells that still work and a willingness to learn

Details about the furnace:
Make/Model: Ruud Silhouette 2
Model Number: UGDJ-10EBRJR
Approximate age: 20 years old

The problem I am facing is that the burners won't stay lit. The startup sequence seems to be ok. With the unit powered on and a call to heat made the following is happening:
Inducer motor comes on
about 30 seconds later the hot surface ignitor lights up
gas valve opens
all 4 burners light up
after about 5 seconds they go out.
blower motor comes on
This sequence then repeats 4 times until the unit goes into lock out mode for 1 hour and I have to reset it in order to try again. During the whole time the Flame LED on the control board never lights or blinks.

Things I have tried / tested:
new flame sensor
new air filter
checked VAC to flame sensor and reading was around 90
checked DC micro amps to flame sensor and that was around 0.1 / 0.2 once flames were lit - this seems bad
checked VAC to gas valve and this was a steady 24 during and after lighting of burners
checked the 9 pin molex connector to the control board to ensure all wires are tight and no cracks or breaks

In reading other posts the next step is usually to check grounding. This is perhaps where I'm lacking in what or how to check. When I look inside the unit I can only see 2 ground wires. One goes from the control board into a romex cable that goes into the junction box and then up into the roof of the basement and over to a ground bar near the main fuse panel in the house. The other ground cable seems to go between the gas valve and the inducer motor. I don't see any obvious ground wires going to the frame of the furnace. Is there something here I'm missing or would this more likely mean that perhaps the control board is bad?

I can provide pictures if this would be of any help.

Thanks in advance for any help.

- Paulo
 
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Old 10-16-19, 08:43 PM
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Welcome to the forums.

The flame LED needs to be on steady for proper operation. Off or flickering means low signal.

Normally just a cleaning of the rod with a green Scotchbrite pad is fine. It's only a piece of stainless steel rod. The rod MUST be engulfed in the flame. If the rod is fully in the flame...... start checking screws on the burner and the control board mounting screws. The circuit goes from the rod thru the flame to ground and back to the module.
 
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Old 10-16-19, 09:16 PM
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make sure the furnace is properly grounded and the burner is clean.
 
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Old 10-18-19, 05:14 PM
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Hello,

So I think I am making some progress here. Looks like it is a grounding problem. If you see in the picture I have attached that when I have the red probe connected to the ground wire on the 9 pin molex connector going into the control board and the black probe connected to the ground terminal then everything works fine and I get 3 DC micro amps once the flames light and they stay on! As soon as I remove the black probe from the ground terminal the flame goes out and the DC micro amps reading goes back to 0. Would this indicate that molex connector is bad or the board is bad or something else?

Thanks, Paulo

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Last edited by PJmax; 10-18-19 at 07:09 PM. Reason: added labeling
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Old 10-18-19, 06:48 PM
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since i don't have a schematic, i don't know what each wire does.

You can test the ground by checking for voltage between the furnace cabinet and line voltage coming in. the ground is connected to the neutral bus bar in the electrical panel and complete the circuit.
 
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Old 10-18-19, 07:10 PM
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You have one probe on the G (fan) terminal. That is not telling you anything.
Check from C to the metal chassis.
You should measure very close to 0 ohms or 0v in the ACv mode.
 
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Old 10-18-19, 07:20 PM
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good catch i didn't look at the picture carefully.
 
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Old 10-18-19, 07:33 PM
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This may not be your exact setup as it's a schematic for the spark ignition and hot surface igniter but the wiring should be similar. You need to concentrate on all the green wiring. It needs to be solid anywhere it attaches to the metal frame. In the circle is an alternate ground bond. The orange is the flame sense circuit. You'd need to open that and put your meter in series on the ua (microamp) scale to read flame sense current.

If your furnace has the 9 pin plug on the board.... and a separate 9 pin connector..... be sure to take apart the separate connector a few times to clean corrosion.

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Old 10-18-19, 07:35 PM
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I just measure VAC from C terminal to furnace frame and got a fairly steady 10. I also measured resistance and as soon as the burners lit it dropped to 0
 
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Old 10-18-19, 08:17 PM
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Temporarily attach a wire from the C terminal to metal frame. See if the furnace works normally.
 
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Old 10-18-19, 08:29 PM
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ok I checked all the ground connections in that wiring diagram and they look good and no corrosion. I took pics and can attach if needed. Measured DC micro amps to flame sensor and it's about 0.1 to 0.2 when burners light and then goes down to 0 when they go off so I know that's bad. I took the 9 pin connector apart and it looks fine, all connections look snug and no corrosion there. One thing I did notice. When I look at the wiring diagram you posted it has pin 1 as empty and the ground in pin 9. When I look at my 9 pin plug it was the ground in pin 1 and pin 9 is empty (see attached pic). Could that be the obvious problem?
 
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Old 10-18-19, 08:32 PM
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"Temporarily attach a wire from the C terminal to metal frame"

when I do this it works fine!
 
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Old 10-19-19, 09:26 AM
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attached the wiring diagram from the back of the door as that might help. It does seem to indicate that the ground on the P1 connector should be on pin 9 and not pin 1 as shown in my connector so if I'm reading that correctly could this be a problem?
 
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Old 10-21-19, 09:53 AM
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ok so problem solved. It was indeed that the ground connector was incorrectly placed on pin 1. As soon as I moved it to pin 9 everything started working again just fine.
 
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