Cad cell high

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  #1  
Old 01-21-21, 08:27 PM
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Cad cell high

Just installed a.honeywell 7284 on my oil boiler. Cad cell starts around 3000 then goes down to 2500 after about a minute. I have had some lockouts this week, boiler hasn't been cleaned for 15 months so it's due. I assume the lockouts are due to a ****ty nozzle. Anyways, as I understand it, cad cell over 1500 means something is wrong. Could this be due to a poor nozzle, or do these cad cells typically go bad after a year?

Thanks.
 
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Old 01-21-21, 09:02 PM
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It should be approx 300 - 1000 ohms when the burner is firing.
Anything over 1600 ohms when firing can cause shutdowns.

it could be a defective cell or a dirty lens.
 
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Old 01-22-21, 01:00 PM
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CAD cells age and resistance rises over time. For a couple of dollar just replace it and keep spares.
But, if resistance stay high then explore other issues.

https://www.supplyhouse.com/sh/contr...hText=cad+cell
 

Last edited by doughess; 01-22-21 at 02:39 PM.
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Old 01-22-21, 02:45 PM
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Before just changing the cad cell which is unlikely to be bad, just moisten a paper towel or cloth with window cleaner & clean the face of the cad cell. It could also be slightly out of adjustment & not be aimed down the center of the air tube. The nozzle could be partially clogged, the burner end cone could be dirty, and the list goes on....
 
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Old 01-22-21, 07:15 PM
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The reason R7284U display CAD cell resistance during runs is they slowly age and go bad.

For a couple of dollars and 5 minutes try it.

The CAD technology is not particularly sensitive to dirt on lenses. Yes sooth an block it.

Changing cell is quick first diagnostic step. Before exploring other issues, replacing with good cell. If problems remain, would then be reason to next explore them.
 

Last edited by doughess; 01-22-21 at 09:45 PM.
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Old 01-23-21, 06:51 AM
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I will say I haven't had a lockout since I put this controller on, could be a coincidence, or maybe that 5s valve-on delay is mitigating the issue that was originally causing lockouts.
 
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Old 01-23-21, 08:51 AM
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Slade8200: Cad cell starts around 3000 then goes down to 2500 after about a minute.
With normal being under 1500 ohms would explore and eliminate reason for high reading.

I just checked resistance in room light of spare CAD cell pins ( not at female spade lugs) and found resistance of 200 to 300 ohms.

Would look for bad electrical connection or something blocking light path to flame.
 

Last edited by doughess; 01-23-21 at 10:19 AM.
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Old 01-23-21, 09:34 AM
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If Slade ends up replacing the cad cell, I suggest replaccing the whole assembly not just the plug in cell. I've found often the problem lies in the socket part rather than the cell itself.
 
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Old 01-23-21, 12:15 PM
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On wires from CAD cell female connector, check the female spade lug connectors which frequently fail to grip male spade tightly.

Female spade grip loosens and become too easy to push on to male spade.

Tighten up female “C_O” gently with needle nose pliers. Close “C” gently at wire end of female, not open end.

Female cad connector round contacts can be closed slightly with small pointed object.
 

Last edited by doughess; 01-23-21 at 01:49 PM.
 

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