[nick26]

Hey everyone, my furnace is used for heat on demand only, not hot water, and the past year (didn't use it all summer) it has had this intermittent problem that trips the reset button almost every day now. When I press the reset button it always fires right up and runs until it hits high temp, and it will kick on as needed, such as if I turn up a thermostat, but almost every day now (wasn't as frequent initially) the reset button trips on it. I had my furnace guy come out and check it out and he looked everything over and said everything was set perfect and if it keeps happening try bypassing the delay valve, and if it still keeps happening get a new oil pump. Well of course it kept happening so I did by pass the delay valve and that made no difference, except obviously the fire starts right away when I hit the reset button. Before I replace the pump I figured I would get an opinion here first. I have read a bunch of threads but they usually involve some other behavior like it shuts off after running for 30 seconds, or sputters, or they have to tap the motor, but mine seems to run perfect otherwise. I also thought if the electric motor on the burner had a bad spot, or the solenoid was bad, then it probably wouldn't so reliably fire up every single time I press the reset button. I replaced all my thermostats with digital ones just in case, but that made no difference (no surprise). Also I replaced the oil filter and put a vacuum gauge on it to make sure it wasn't getting choked (and re-bled it) and that didn't matter. So I was wondering if anyone wanted to venture a guess at what the problem might be or at least some tips for trouble shooting it? I am comfortable with the multi-meter if anyone wants to tell me to what to check?

Thanks for your help!

To give you some background info about my system, here is some model info:

 

[beenthere]

A few possibilities.
Weak transformer that gets weaker as it gets warmer/hotter.
Nozzle to always spraying a good pattern.
Cad cell weak or misaligned(guessing the tech checked it to make sure its clean).
Cracked retention head.

 

[nick26]

My furnace guy replaced the nozzle and made sure it was spraying well too, and he adjusted the electrodes slightly closer, but none of that seemed to make a difference.

I found this link: http://www.beckettcorp.com/scripts/filesearch/techinfo/664824.shtml and tested my CAD cell. It measures just over 300 Ohms when I point it at the light and just under 2000 Ohms when I cover it with my finger. The link says it shouldn't be higher then 1600 Ohms, and around 300-1000 ohms normally, but I wasn't sure if they were talking about it when there is no light too. Are they saying it should be 1600 Ohms max ever?

If the CAD cell is ok, is there any trick to testing a transformer? If I test the voltage, then let the furnace run for a few mins and then test it again, would I possibly see a difference, or it has to be under load to tell?

Is there anyway to get any useful info out of the aquastat? Mine never displays anything except the temp, despite error codes listed on the bottom of the cover.

Here is a pic of my cad cell and transformer:

 

[techpappy]

I had the same problem with my Riello oil burner and it turned out that I just had to tighten down the mounting screws of primary control. It had me baffled for a while and I am an oil burner tech with Riello factory training.

 

[nick26]

I had the same problem with my Riello oil burner and it turned out that I just had to tighten down the mounting screws of primary control. It had me baffled for a while and I am an oil burner tech with Riello factory training.

I am pretty sure that is not the problem in my case, because I have taken the primary control off a couple times just to make sure all the wire nuts were tight, and I always tightened it back down. Do the primary control boxes go bad ever? Would it have this kind of symptom?
Thanks

 

[old_squid]

When you push the reset and the burner fires up like nothing is wrong, does the flame rumble like maybe there is excess oil in the chamber?

Do you or have you ever oiled the burner motor?

 

[nick26]

When I press the reset button it doesn't rumble at all, it just kicks on and purrs pretty well.

I have not oiled the motor at all, and been in the house for about a year and a half, so I don't know the history before that. Can I use the same oil that is used to drop into the circulator pump?

 

[old_squid]

With no rumble on startup after the reset is pushed indicates (because you already eliminated the delay valve and it still failed) that the oil pump is not pumping oil into the combustion chamber. If oil had been sprayed in there with no light off you'd of had a noisy/rumbling light off when it started the next time from the excess fuel oil.

Reasons for oil pump not consistently delivering oil:
1) delay valve not opening, which you already (I understand) eliminated
2) intermittent oil to pump or failing oil pump
3) failing coupling between motor and pump
4) intermittent problems with start switch in motor. burner motors have a mechanical centrifical start switch in them.
5) intermittent problem with relay contacts in primary control

My bet is on #4. And a good possibility of #5 because of #4 happening first.

It's a common problem with oil burners having the symptoms you're explaining. The problem usually occurs when someone over oils the bearing on the end of the burner motor and gets oil inside the motor onto the contacts of the start switch. This lack of good contact stops the motor from starting and causes a lot of amps to flow through the small contacts in the primary control arching and burning them.

I'd replace the burner motor and the coupling (only because they're not that expensive and as long as you have things apart. I'd also replace the primary control.

If you feel the need to oil the bearing on these motors use only 30 weight non-detergent motor oil and limit the oiling to 3-5 drops a year after the motor is 3 years old. The motor doesn't work that hard and the actual hours of running time per year isn't that much.

 

[nick26]

Great thank you for your diagnoses! I'll post back with how it goes.

4) intermittent problems with start switch in motor. burner motors have a mechanical centrifical start switch in them.

Could this kind of failure ever cause it not to fire up right away when pressing the reset button? I would have thought it might, but it does always immediately fire up when I press the reset button.

I'd replace the burner motor and the coupling (only because they're not that expensive and as long as you have things apart. I'd also replace the primary control.

The primary control doesn't seem to be cheap, so I was going to start with just the motor and coupling. How important is the primary do you think? Does the mechanical switch in the reset button wear out?

If you feel the need to oil the bearing on these motors use only 30 weight non-detergent motor oil and limit the oiling to 3-5 drops a year after the motor is 3 years old. The motor doesn't work that hard and the actual hours of running time per year isn't that much.

I never really considered oiling it, maybe the furnace guy did when he was over, I don't remember. Is that something that is recommended to do or not to do based on your observation of it causing problems?

Also I found this site that has the motor I need: http://www.patriot-supply.com/
Is there any other sites that people around here recommend?

 

[nick26]

Ok, so I replaced the motor and the coupler yesterday, and it tripped again today anyway, so that wasn't it. What's next? Primary control? Oil pump?

 

[old_squid]

Great thank you for your diagnoses! I'll post back with how it goes.


Could this kind of failure ever cause it not to fire up right away when pressing the reset button? I would have thought it might, but it does always immediately fire up when I press the reset button.

In my experience the motor will run and the unit will fire up perfectly 90% of the time.

The primary control doesn't seem to be cheap, so I was going to start with just the motor and coupling. How important is the primary do you think?

The primary control is what powers the motor, high voltage transformer and privides the safety shut off if no flame or a bad flame is sensed. I'd call that important.

Does the mechanical switch in the reset button wear out?

Not that I've ever seen

I never really considered oiling it, maybe the furnace guy did when he was over, I don't remember. Is that something that is recommended to do or not to do based on your observation of it causing problems?

After say 3 years of the motor being new, 3-5 drops of 30W non-detergent oil is plenty.

Also I found this site that has the motor I need: http://www.patriot-supply.com/
Is there any other sites that people around here recommend?

In your later post I see where changing the motor did not resolve the issue. Not being there I'd lean towards changing the primary control.

 

[nick26]

Quick question... I got the new primary and I was about to hook it up but I wanted to make sure it should be wired exactly the same way as the old one, as far as a jumper across the T thermostat leads and the other wires going to the CAD cell which I assume has no polarity?
Thanks,
Nick

 

[old_squid]

Correct

 

[nick26]

Ok, that is what I did, and so far it has run for 24 hours without tripping, which is looking good, but I don't want to get my hopes up just yet. I will keep you all updated.

 

[nick26]

So it's been a week and it hasn't reset once, so I guess I can consider this problem fixed! Thank you very much for everyone's help, especially old_squid!