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rodney23 02-07-2011 11:16 PM

Intermittent furnace lockouts, fouled nozzles, combustion air, and cold basements
Hey all,

So, recently I've been going through an issue with my furnace. Its an oil fueled Weil-Maclean (spelling?) with a Carlin burner. I started experiencing intermittent latch-ups (red light, resets with the button and seems to start back up). Its been happening early-mornings, but the reset will usually last the day.

We had the furnace serviced. They cleaned it out, replaced the nozzle, replaced the oil filter, etc. It was fine for a few weeks... then started acting up again with more intermittent latch-ups. They came back out today and found the nozzle was fouled up again (carbon deposits). The did a bunch of other testing while they had everything apart. The tech noticed the blackened insulation above the furnace (soot) as well as the dusting on the top of the furnace just below the interior vent of the furnace exhaust.

He then played with the basement door to the outside and could feel the pressure created when he opened/shut the door. He recommended a combustion air intake (we do not have one currently). I'm guessing he suspects less than ideal combustion could be causing the carbon deposits due to no air feeding the combustion process.

My first question for you HVAC guys.... Does this sound like a plausible cause of the latch-ups on the furnace as well as the fouled-up nozzles? I just want to make sure I get a second opinion before I go cutting holes in my basement.

Given they're correct, obviously the next step is to install a combustion air vent. Here's where I'm concerned. If I open up the small basement windows or door... the draft coming into the house from these openings is significant (probably confirms that the furnace was starving for air). I'm worried that if I go and add the vent... my basement is going to become a frozen zone (we're in NH btw).

My basement level is a 2-car garage connected to a finished area connected to the utility/storage room. This is all on the same slab level, with no door in-between the utility area and finished portion (there's just an entry way connecting the two by the stairs to the main floor). So... any air entering the utility area will likely just flow into the finished area, chilling everything.

I've seen the ideas of putting the end of the combustion air pipe into a bucket or looping it up into a "J" shape... but I'm not sure that would slow the air that much as I believe the negative pressure of the house would overcome those mitigation efforts. Is my only solution to that problem to identify where the air might be escaping the house in an upper floor (a leaky flu, attic fan louvers, attic stair access, etc.), and therby hoping to keep the leaky spots from creating a negative draft that would suck more air in constantly?

Am I missing anything? I just don't want to solve one problem and cause myself another by now having a freezing basement that has to be heated to counteract the fact that the furnace can't burn efficiently without the air that's now causing the cold! :)

Thanks all!

beenthere 02-08-2011 03:50 AM

Look for and fix the leaks in the upper floor area first. Then use the pipe in a bucket to prevent excessive air infiltration from the combustion intake pipe.

rodney23 02-09-2011 11:53 AM

I guess no matter what happens, if I add the vent or not... I should be plugging any leaks on the upper floors regardless to help keep heat in the house instead of flowing out.

So... thanks, but either way... would the incomplete combustion lead to a fouled nozzle like they were theorizing? Or... is really the only way to end up with a clogged nozzle to have bad, gunky fuel?


beenthere 02-09-2011 07:04 PM

Incomplete combustion can cause it. Depending on how bad it is.

rodney23 02-12-2011 11:14 PM

Ok... so... did some experimenting with air flow.

In order to test the theory that the furnace wasn't getting enough combustion air I opened the small window in the basement. I had it open enough that it was a 1 ft sq. worth of air flow... more than what most vents would bring in.

Sure enough... the furnace still goes into lockup. Since last Tuesday (5 days ago), its now repeating the latch-up at least 2-3 times a day. It wouldn't be such an issue except when it does it at 1 AM and I wake up to a 55 degree house and my wife and 2 year old are freezing!

According to the documentation on the burner... "If flame is not established within 15 seconds (TFI) of oil valve actuation lockout (everything off) will occur. Lockout is indicated by a "solid on" red LED and closure of the alarm contacts". If I'm not getting flame, what's going on?

The lock-up seems almost random. We had the furnace on and running for over an hour this morning while trying to get the house back up to temp. We noticed it wasn't running... but the thermostats were calling for heat. We checked and it was locked out again. It always seems to reset and run without much of a problem... until the next lock out at some point later.

Could it be bad oil? I have a filter on the tank, and the pressure gauge is in the green... so I don't believe its a flow problem.

If its another clogged nozzle... could the bad oil be good enough to flow through the filter yet bad enough to clog up the nozzle and shut down the burner? I thought the filter was supposed to keep junk out of the system and the nozzle. I looked at the nozzle they took out. The gold mesh portion of the nozzle is black and clogged

Any help is greatly appreciated! I'm already into this for about $350-400 worth of service calls... I need to get to a solution before I'm broke or I freeze!


beenthere 02-13-2011 04:22 AM

The intermittent lock outs can be caused by a weak ignition transformer, a bad/dead spot in the burner motor's start windings, weak or dirty cad cell(its what sees the flames), a weak safety circuit in the primary control. Along with another bad nozzle, improperly set electrodes, and a few other things.

When you reset the control. Does it light with a puff smoke?

rodney23 02-13-2011 09:38 AM

Where would I see the puff of smoke come from, the flap valve between the back of the furnace and where it enters the chimney in the wall? I can't say I've seen any smoke come from any area as I've watched it re-start. But I haven't really been looking for that.

I would have assumed that the tech that was here for 2.5 hours the other day would have checked all those things you mention, but... their bill mentions they checked the following:

1. Pump screen
2. Oil line vacuum
3. Venting
4. Combustion Air
5. Ignitor
6. Fuel pump pressure

So... it doesn't specifically call out that they checked the CAD cell, start windings, safety circuit or electrodes. I'll have to talk to them about that on Monday.

Thanks for the help beenthere!


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