I have a Beckett AFG burner, the furnace is power vented and has a V1 head.
The burner starts up then after about 10 sec trips safety. I have replaced electrodes and nozzle, thoroughly cleaned head and air tube. Yesterday I had a service man come and adjust air using CO2 sensor and a probe to check conditions in pipe. He stated unit was running very close to perfect, yet a short time it started kicking again. He checked transformer voltage and stated it was good. The furnace was serviced 3 months ago but I know now that the electrodes were never changed so now I am wondering if oil filter was changed.
The furnace always stay on after I reset the safety switch.
Any suggestions on what to try?? I have set all mechanical specs according to Beckett manual... please help me

Thanks
Bob

Cad cell detector?
Intermittent safety control.

The trip on the safety usually indicates that the cad cell is weak or not seeing a good flame signal. Wipe off the cad cell clear cover with a soft cloth or just replace since they are so cheap. Also make sure the sight port is clear and lined up with the cad cell so it gets a full view of the flame.

Usually on a trip of the safety the oil filter and electrodes do not come into play as long as the flame is good every time it starts. Electrodes last for years unless they are cracked at the insulators. All you have to do with electrodes is make sure the to measurements are maintained. Space back from nozzle and gap.

Try hooking up a switch across the thermostat terminals after you remove the thermostat wires from the thermostat terminals. This way you can switch the burner on and off manually. (NO the power switch will not work for this test it has to be done on the thermostat terminals.)

Get yourself situated at the burner where you can see the flame and manually kick it on and off a few times and see if it trips. Post back with results. I am looking for false start signals or electrical chatter caused by the thermostat or any other switch/relay on the power venter proving circuit.

I unhooked all thermostats and had unit call for heat via hot water temp and unit still tripped. I have a flame and cad cell was already wiped and line of site is good. I had water temp call twice and both times it tripped, I need to wait a little and I will try jumping out my only old style thermostats . All my mew ones a re digital and I turned them off.

I just jumped out my only mechanical thermostat and when the furnace fired it tripped. AS soon as safety delay was timed out I reset it and it started up. Why does it always stay on the second time?

That is a good question and I do not have a answer for that. Was the burner firing when it tripped? The cheapest next step is to replace the socket/wire assembly for the cad cell. This is called the cad cell holder. Since the signal from the cad cell can be weak and cause this problem and item connected with the cad cell is subject to problems. You can check the cell see next paragraph.

To check the cad cell use the below instructions. What you are going to do is remove the cad cell wires and have a jumper ready. Then fire up the unit and put a jumper across the cad cell connections on the safety control (read cautions in instructions). The with a OHM meter you are going to take a reading of the cad cell in OHMs to see if it is good or bad. Post back with results.

See page 2 for exact instructions for testing.

http://www.white-rodgers.com/wrdhom/pdfs/instruction_sheets/0037-2649.pdf

When I disconnected cad cell reading was basically an open. Once furnace called I jumped out cell , reading on cell was 900ohms steady and while it was jumped furnace did not stop

Usually anything below 1000 Ohms is golden so that looks good. Unless the burner is not igniting and burning when the safety trips the only thing left is the safety itself.

Can you get the exact brand and model number off the safety control? If so post it and I will try to look it up.

The safety is a Honeywell R8184G 1427. One other question, where the nozzle goes out of unit there is a gauge with 0-? The V1 head states to be set at zero but there is also a slide at nozzle it looks like it has always been in the center but that can change depth of the whole burner unit by a half inch. I never touched this but it looks like the only way to measure the distance is to remove the whole unit off the furnace

Check page 3 for cad cell honeywell

http://customer.honeywell.com/techlit/pdf/PackedLit/60-0164.pdf

Primary safety Honeywell

http://customer.honeywell.com/techlit/pdf/PackedLit/69-0618.pdf

Beckett Manual

http://www.beckettcorp.com/protect/techsuppt/product-manuals/6104BAFGR04.pdf

If it will not let you DL the manual then you will have to register and then DL

Here click professional then register

Beckett Corp. | User Login (http://www.beckettcorp.com/protect/auth-industry2.asp)

I tried swapping out cad cell and wires... ng. Everyone told me to try primary which I did.
Unfortumately neither of these solved anything. I spoke to a man at beckett and said pull out cad cell and when furnace turns on shine a light on it , I guess he is thinking we are not getting light even though I told him I jumped it out and it read 900ohms. He is wondering if it has anything to do with my powervent.

Well everything has checked out on the burner so far so the power vent is next. The only problem with that is the fact that we jumped the thermostat wires out on the safety I believe and that should have eliminated the power vent relay if so equipped.

I just spoke to someone fromFieldControls the maker of the power vent. He told me to check for blockage in the tube to the pressure switch. I took my compressor and blew it out and 3 x's now furnace has started up. It ow starts almost exactly when burner does which is how the guy from Field Controls said it should. Before this there was always a 30 - 45 sec delay before burner would try. I will keeep you posted how it works...
Thank you for all your help , I let you know in about 3 hrs if it is still good
Bob

It's now been about 3 hours and so far so good!
HVAC1000... again thanks for yout help
Bob

Good deal. All the worry over the burner and it was a plugged tube. LOL That would have been a fun one to work on if I could have been there to see the power vent setup it might have been quicker to fix. The old field control power draft system had a relay that would trip to start the burner and now they have gone to a pressure switch. Interesting. Hope it stays running.