Cad Cell keeps Tripping

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Old 04-27-10, 07:22 PM
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Cad Cell keeps Tripping

Hi,
I have a Beckett burner Model AFG w/
Carlin Igniter, Honeywell control on a Vaillant Boiler model F70W-4-PP

My problem is that the red trip switch keep triggering. I have replaced the following:
F head plate
nozzle (same as one previously in there)
Fuel Filter
High pressure line
Gaskets
Line from tank to burner

I have done a total cleaning and set the spacing of the electrodes and nozzle, pump bled. The cad cell is clean and checks out on ohms meter. Flame is clear and bright thru eyeglass.

A friend suggested that I may still have some air and that the pump is giving burps in the spray causing the lockout and the problem may subside after continued resetting for a few days. Is this a common opinion or does anyone have another area I can look at as the problem?

Thanks
 
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Old 04-27-10, 07:49 PM
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Motor?

When you press the reset I presume the burner fires up. If so does the flame look "normal" or is it more yellow to orange?

Have you checked the cad cell resitance while the burner is running & if you have what ohm reading did you get?
 
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Old 04-27-10, 08:01 PM
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The flame doesn't seem to be orange. It might be a slight bit yellow but I don't know for sure as I just cleaned the sight glass during the cleaning and don't have anything to compare to. I tested the cad cell disconnected. I will have to check again as I forget what reading I got.

Now, since last time I posted I checked the blast tube and found some fuel in the bottom of the blast tube and a little burn residue. I haven't checked the ignitor. Could that be the problem? If that's possible I can do the screw driver test over the coils (using the rubber gloves of course)
 
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Old 04-27-10, 08:22 PM
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If I do an Ohms test on the cad cell terminals while it running I'm getting 1500.
 
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Old 04-28-10, 06:30 AM
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I read some other articles, should I be getting more of a blueish flame?
 
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Old 04-28-10, 04:44 PM
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Blueish Flame

You most definately DO NOT want a blueish flame. An ohm reading of 1500 is well on the high side & quite possibly the cause of your lockouts. Normally I see around 500. If you don't have combustion test equipment I would not suggest you make any adjustments to the burner.
 
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Old 04-28-10, 05:31 PM
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Grady, can you go over the proper way to measure the resistance of the cad cell? Is it as simple as just putting the ohmmeter on the terminals when the burner is running?

(I really like the new primary controls that have the cad cell test feature built in... a push of the button, a few LED blinks and you know the resistance... schweeet)

By the way Dcad, when you cleaned the boiler, did you remove the metal plates on top that are held by spring clips under the draw bolts and clean the flue passages between the combustion chamber and the heat exchanger? Very important to do so, they get plugged fairly easily on these boilers.
 
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Old 04-28-10, 06:53 PM
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I replaced the CAD cell. The new one while connected to the terminals and boiler running reads 1200ohms. I did not make any adjustments to air intake on the burner nor plan to as I don't have the tools to measure the airflow or want to spend the money on them.

NJ Trooper - No I haven't cleaned that area yet. I only have small blocks of time to work on this so I've been taking one thing at a time while trying to keep hot water going. Burner is all clean and I cleaned the stack to the chimney but still need to clean that area. When I changed out the Cad Cell I noticed it was open between ignitor compartment and Honey Control where the wires go thru. Looks like there is supposed to be a grommet there. I did see some puddy below the wires so I reused that to pack the hole. I would imagine all these little things will make a difference.

I will let you know if the new cad cell make a difference.

UPDATE: The boiler got up to temp. dropped down to low limit and locked out again so it's not the cad cell. I'm guessing the only things left are: Honeywell control, ignitor or electrode assembly. Where do I go from here?
 
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Old 04-28-10, 08:31 PM
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Something tells me that you can't really get an accurate reading of the CAD cell while it's connected to the primary control... but I could be wrong about that...

The control should only be locking out when there is a flame failure... when the burner tries to light, but within the lockout time the cad cell doesn't sense flame.

So, just to clarify, you say that when it 'drops to low limit' it locks out... do you mean that the burner fires, or tries to fire, and then some 15-30 seconds later it locks out?

Cleaning those flue passages is very important, because if they are plugged up, the exhaust has nowhere to go. If they are really plugged up, this could well be the reason for the flame failure. If there is no air getting through the boiler... the flame will be really crappy and not bright enough to keep the control from locking out. But, you did say that the flame was bright, so maybe that's not the problem...

Personally, I think suspecting the cad cell is probably chasing a ghost. The one thing that you didn't mention you changed was the STRAINER in the fuel pump... did you change that?

When you changed the line to the tank, you did NOT use any compression fittings, correct? You used all FLARE fittings, yes?
 
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Old 04-28-10, 09:29 PM
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I sat and watched a couple cycles to see what it’s doing so I have more details. The first time it hit the low limit, the fuel pump did not come on, the lockout just kicked in and the red light went on. I’ve found that just pushing the reset button once does not restart it either. It’s like the first time you push the button, the button clicks down but then you have to push it a second time and then the button clicks down to a lower level and the burner starts up. The second cycle I watched is even more interesting. It got to the low limit, fired up like it’s supposed to for maybe three seconds, with flame but the button tripped and shut down the burner, the red light comes on, a few seconds later the red light goes back off. Then a little while later it’s back on again. Is it possessed or faulty? I’m thinking I have a bad control. What do you think?
 

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Old 04-28-10, 10:35 PM
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Yes, it does sound pretty whacky...

Not sure what you mean by "the fuel pump did not come on" ...

The fuel pump is driven off of the motor, as is the blower. Is that what you mean? that the MOTOR didn't run?

Have you checked the PUMP COUPLER ? inside the burner? (you need to drop the motor to access it)

and, did you, or did you not change the strainer in the fuel pump?
 
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Old 04-29-10, 07:39 AM
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Yes, I did mean the motor. I could not hear any sound from the motor just before the control tripped. Yes, I checked the coupler, in fact I changed it out during the cleaning (forgot to mention that). This unit has the mechanical air vent and I cleaned that too and slides easily - good springs. I did not change the strainer on the pump as it was in excellent condition. It had a tiny bit of residue that I cleaned with a tooth brush and DW40. Switch keeps tripping now while it tries to get up to temperature. I have to push the button several times before it finally engages to turn the motor on. I ordered a new control.

On your other question about the new fuel line to the tank, I have a flared end fitting before the filter (filter is at the pump) and on the tank side there is a compression fitting at the tank valve. I just replaced the compression ring and female end on fitting. I'd like to change that out but it is part of the valve but I made sure the fitting is snug. - no leaks.
 
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Old 04-29-10, 10:58 AM
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This unit has the mechanical air vent and I cleaned that too and slides easily - good springs
If you are talking about the infamous "Inlet Air Damper" assembly, a centrifugally opening inlet air shut off device, the best advice anyone can give you is "Get rid of it!". You may have the last remaining one in existence. If you do decide to dispose of it, you can replace it, and the short coupler that it uses, with a 'standard' length coupler.

I just replaced the compression ring and female end on fitting. I'd like to change that out but it is part of the valve but I made sure the fitting is snug. - no leaks.
The best advice anyone can give is "Get rid of it!" ... change the valve if you have to. Yeah, I know, it's not leaking... famous last words. I know, you don't see any oil coming OUT, but that's not what you are really concerned about... of course there is no oil coming out, there's no pressure inside! when the burner is running there is a VACUUM in that pipe, and air molecules are much smaller than oil molecules and the air can leak IN, and no oil OUT... compression fittings on a fuel line are a big NO-NO...

Everything you describe about the primary control does sound as if it's bad though... there is one more thing... it is possible for the motor to have 'flat spots'... bad segments on the winding... and if the motor happens to stop at one of those points, it may have trouble starting up again. This would usually be a very random lockout though, and you are saying this is happening with increasing frequency... still, something to keep in mind.
 
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Old 04-29-10, 11:21 AM
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The new coupler I bought came with the end for the motor and I took it off for the Air Damper - correct size. I can put that end back on the coupler and use it after removing the Air damper. Question - Does the airflow have to be re-calibrated if I remove that damper?

I agree with you on the compression fitting. I've never had good luck with those type fittings and never use them if I don't have to. This problem did show up before I touched anything (I understand it can still cause problems on it's own) and I do wish to replace that fitting at the tank. Hard to change the valve when it's holding back the fuel though. Problem right now is that the tank is old and if I mess with that fitting at the tank before I'm ready to change out the tank I might have a giant mess on my hands because the tank is very old and needs to be replaced. I'm waiting to get the oil level low enough then I will change the tank and fittings out (my next big project) If I put a gauge on the high pressure line, won't it tell me if I have a vacuum leak? (temporary check until I can change the tank & fittings.)

If the controller doesn't fix the problem and the next step is the motor, might it be worth it to just buy a whole new burner assembly? I can get a new up to date assembly for around $320.00 complete with the updated controls. My only concern is I assume I would have to call someone in to adjust the air flow unless I can just set it exactly as the old one if the fuel flow is the same?
 
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Old 04-29-10, 02:05 PM
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Yes, you would/should check/change the air setting after removing that damper. So, if it seems to be working OK for now leave it alone.

The valve you are talking about is the valve at the bottom of the tank? Yeah, I guess it's best to leave that alone for now also. No, you won't see a vacuum leak on the high pressure side.

I think the control is probably the problem.

I don't really see the point in replacing the entire burner assembly, especially on that old boiler. The only reason I can think of for replacing that burner would be if you ran a truck into it and broke the housing... all the other parts are replaceable.
 
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Old 04-29-10, 08:18 PM
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Regarding the air inlet damper: Removing it is not as easy as it would seem. In order to get it out one must also remove the air guide (plastic cone inside the burner body) which is held in place by 3(?) phillips head screws. Be careful as not to break the guide or it's plastic "ears".

Cad cell resistance needs to be checked with the leads disconnected from the primary. To keep the burner running simply temporarily install a jumper across terminals F-F. You can also check the primary safety circuit by installing a 1,000 ohmm resistor across F-F while the burner is running. If the burner locks out, the primary is bad. Another crude but often effective test of the primary is to rap the side of it firmly with the handle of a screwdriver while the burner is running. If the primary locks out, replace it. (weak relay coil)

If the burner motor did not start with the first reset I suggest checking the motor. Presuming the motor to be of the split phase type (no capacitor), disconnect & remove the motor. Place the motor (shaft up) on a bench or the floor. Attach one lead of an ohm meter to each motor wire. Set the meter to its lowest range & note the reading. Lift the motor gently by the shaft while watching the meter. Any significant change in the meter reading indicated a bad start switch in the motor.
 
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Old 04-29-10, 09:18 PM
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Grady,

I tried your screwdriver test on the primary and the relay coil is very, very weak. My first try was a very light tap and it trips. Even a flick of the finger trips it so it is looking more and more that this is my problem or at least part of it. I just checked the shipping on the new primary and I should get it in tomorrow so I will post my results after I install the new one.

On the air inlet damper, I did take it out during cleaning and found it very difficult to get back in as the plastic cone is fragile and you have to hold up the damper in front of the cone while separately holding the plastic cone while putting in the screws. Easier if you have three hands.

If I can solve this problem (mostly with your help - NJ Trooper and Grady) next I will be splitting one of my heating zones into two zones and when the fuel gets low enough attack the new fuel tank project then be very satisfied with the heating system. Did I mention that the pressure relief valve exhaust pipe was held together with duct tape dripping down all over the zones pump. That was the first thing I fixed. Joys of a new home with a whole new can of worms.
 
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Old 04-30-10, 03:45 PM
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Well it's looking like a two thumbs up on the primary being the problem.

I put the new one in this morning and have not had a single shut off and the boiler is maintaining temperature. It's so nice when things work. A big thank you to both NJ-Trooper and Grady. By the way NJ-Trooper, are you a New Jersey State Trooper? I tried the test for RI Trooper three times and did get accepted the third time but was already in a new career (was a long time ago now). A very good job. Thanks again guys.
 
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Old 02-10-13, 05:13 PM
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Hey everyone, I was just reading though this thread. I have similar issues with my Beckett AFG oil burner tripping. I have replaced the CAD cell, nozzle, electrodes, transformer. It will run for usually 1 or 2 cycles then shuts down. I can then go press the red reset button that is attaced to the right side of the burner (I think this is the controller but it is just a electrical box with an old cirecuit bored in it, Honeywell grey cover) and it will kick right back on.

I read in this thread that the "Primary" was the problem. Is this the same as the controller?

Something else that is weird that I think someone mentioned here is that the small transformers on the controller. I dont even really have to push the red reset all the way. Sometimes you just get close to the red button and it kicks back on.. Kinda like magic. Any ideas on what I can do? Tahnks!!
 
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Old 02-11-13, 07:15 AM
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I read in this thread that the "Primary" was the problem. Is this the same as the controller?
The control that sits on top of the 4" junction box above the burner is properly called the "OIL PRIMARY CONTROL".

Sometimes you just get close to the red button and it kicks back on.. Kinda like magic. Any ideas on what I can do?
If the burner cuts out and then back on without even having to touch the button, then obviously there is something wrong with one of the controls... just be fairly warned that the problem could be elsewhere... I'm not saying that the problem is NOT the primary control, but I'm not saying that it IS the primary control either.

It could be a loose wiring connection, even a bad aquastat on the boiler...

One would have to do some testing to determine which it is.

I would say that it sounds 'likely' to me that the problem is the primary though...
 
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