My parents live near Malone, NY, near the US-Canadian border. Their house is an old 2-story farm house with an oil-fired forced hot air heating system. Seven years ago, they had a Comfort-aire Patriot 80 oil furnace installed, model OLRA125D5-2. This furnace has a Beckett AFG burner unit. They do not have an AC system. The thermostat is a recent Honeywell manual unit (not programmable). Until last month, when their heating company came in to do the annual cleaning and tuning, this furnace worked fine. Since the cleaning last month, my parents have observed the following problem:

1. Thermostat calls for heat
2. Oil pump pressurizes
3. Burner ignites normally (no banging noises, no delayed ignition)
4. Circulating fan comes on.
5. Warm air blows out from floor registers as expected. No smell noticed.
6. Once set temperature is reached, thermostat sends shut-off signal.
7. Burner unit shuts off normally and quickly. No rumbling or burbling heard.
8. Fan continues to run for 1-2 minutes. At this point, a strong smell of burnt oil is noticed at the floor registers. No visible smoke is observed.
9. Fan shuts off.
10. After a couple of minutes, fan comes on again for 10-20 seconds. No smell is detected from floor registers at this point.

The heating company (which installed the furnace originally and has maintained it ever since) has been back several times and cannot find the cause of the problem. No CO has been detected by my parents' detectors or by the heating company, or by the fire department. The technician suspected a hole or crack in the heat exchanger and did a smoke bomb test, but no smoke was seen coming out of the registers. My parents noted that the tech who did the cleaning (a younger guy) was in a hurry and did a lot of banging around while he did the work. They also found that he used the wrong air filter insert (force fitting one that was almost the right size) and are nervous that this guy somehow damaged the furnace. The senior tech who has been trouble-shooting the problem since is trying to make it right and is baffled (his word) by this problem.

The oddest thing about this situation is that the smell only occurs *after* the burner shuts down and while the fan continues to circulate warm air. As I understand it, if there was a crack or hole in the heat exchanger, you'd expect to smell the burnt oil odor throughout the entire heating cycle.

I read through some of the other odor-related threads here but didn't find any that described the "delayed smell" situation my parents have. Any insights or ideas you can share would be greatly appreciated!

 

The reason the blower motor is energizing again after running for 1-2 minutes after heat is satisfied is the limit adjustment on the fan/limit switch is set to high. It needs to be lowered a small amount.
As for the oil smell, the only thing I can think of is the fuel oil shutoff is slow allowing some fuel to continue after the igniter has shut down. This oil is vaporizing in the firebox and somehow getting into the return air duct in the basement and out the heat registers. Hope this helps.

 

beelzebob, thank you for your comments! I was wondering if slow oil shutoff could be in play here. BTW I talked to my father after posting yesterday, and he mentioned that when the junior tech was doing the cleaning, he disconnected the supply line that runs between the filter and pump. The burner came on at that point - because the guy hadn't shut off power to the furnace! - which surprised the tech. When he jumped up to hit the emergency switch, he dropped the supply line on the basement floor, which is dirt, not concrete. My father didn't think that the guy flushed the line before reinstalling it, so now I wonder if some dirt got in the line and has now clogged the oil shutoff valve so that it doesn't close properly.

 

Dirt in the pump is possible but not very likely. If the pump in one of Beckett's Clean-Cut units with a fuel solenoid, solenoid failure is not an uncommon problem.

 

I'd be slightly concerned about how the smell got into the ductwork too.

 

PJmax, my father and I are worried about that, too, as that usually means the heat exchanger has a hole or crack. What we can't figure out is why the smell occurs only after the burner shuts off. If the heat exchanger had a crack or hole, wouldn't we smell it whenever the furnace is running? My father and I have even thought about a crack/hole in the heat exchanger that opens up only once everything is good and hot due to thermal expansion -- is that possible??

 

Grady, thanks - the burner does have a solenoid, so I'll mention this to my father so he can alert the technician.

 

Cracks usually do open with heat. Is the furnace power vented or does it exhaust into a chimney?

 

Hi Grady, the furnace exhausts into a chimney.

 

I believe you are getting what is often called "after drip" which is fuel dripping into the hot chamber after the burner has shut off. There can be numerous causes but a few of the most common are: The house being under negative pressure (try cracking a window in the basement); Bad fuel pump (already touched on that); Cracked burner end cone; Incorrect "Z" setting; Incorrect nozzle, pump pressure, or air adjustment.

 

Grady, thanks! I will pass this along to my parents ASAP.

 

Hi everyone -- my parents' Patriot 80 furnace is still misbehaving as described in my original post. Last week, the service technician was out at their house again, and he noticed that while the air handler fan was running, the air handler access panel was being sucked tight against the furnace housing, as if the air pressure in the air handler area was lower than the basement air pressure. The tech thought this was odd, so I wanted to check this with the experts on this forum.

My parents unit is a "low-boy" design with the return inlet and supply outlet on the top of the unit. The flue pipe exits horizontally out the back of the unit. Below the flue pipe is the air handler access panel. This diagram shows a cutaway side view of a typical low-boy furnace: inspectapedia.com/heat/0711s.jpg

And this site has several pictures of the Patriot 80 low-boy: Comfort-Aire OLRA125-D5 Lowboy - Rear Flue - 140,000 - 154,000 - BTU Oil Furnace

If the pressure differential noticed by the tech is not normal, what should we be looking for in terms of possible causes?

 

The most common causes for this are: Return ducts too small; closed, blocked, or otherwise restricted return vents; dirty air filter; or highly restrictive air filter such as these high dollar pleated 1" filters sold at most big box stores.

The reason your folks are getting fumes is the blower is pulling air from where ever it can. In this case it's probably coming backward down the chimney. This is very easy to prove with draft gauge. If you mention this to the "tech" & he looks at you like you have three heads, grab the nearest weapon & chase him off. BASICS, BASICS, BASICS

 

Hi Grady, thanks for writing back so quickly - on a Sunday, no less! I talked with my father about your advice, and we agree that it sounds like he needs to get the tech back out to the house to focus on troubleshooting and correcting the air restriction problem. Then, if that doesn't resolve the odor problem, we move on to other possibilities.

 

Did you ever try cracking a window in the basement? If so, what was the result?

 

Sorry for the long delay in updating this thread, but I finally have an update.

• Opening the basement window made no difference in the symptoms.
• Opening the access panel to the air handler immediately reduced the presence of the odor. Unfortunately, the barometric damper is only a couple of feet away from the air handler, so we think (with the access panel removed) the air handler was able to open the damper and draw smoky air into the house.

To me, this says that the next action that has to be taken is to diagnose and correct the insufficient return air flow. As I mentioned in my original post, my parents live in an old farmhouse, and we think it was retrofitted for forced hot air heat sometime in the 1950's. The ductwork was not installed according to any standards or practices, and whenever a new furnace was installed, the installers just hooked up to the original ductwork without re-evaluating the design of the system.

In addition, about 25 years ago an addition was built and additional ducting was installed to heat the new rooms. The builder, who it turned out was not an HVAC pro, used flexible duct tubing, and I think it's at least possible that one of those return ducts may have collapsed, reducing return air capacity.

The service tech who has been trying to solve the odor problem suggested cutting a hole in the return duct down in the basement near the furnace as a way to quickly increase return air flow. I think this is a bad idea (wouldn't it draw exhaust air as happened when we opened the air handler access panel?) and told my father that he needs to get the heating company to evaluate the existing return ducting for obstructions (and correct anything found), then calculate the correct return air capacity needed and modify the ducting, probably by installing additional return ducts, to satisfy that. After the air flow problem is fixed, then the odor problem can be addressed, assuming the ducting fix doesn't eliminate the smell.

Am I on the right track here?

By the way, where my parents live in Northern NY State, there are very few HVAC installers in the area. Also, there's an unspoken tradition up there that you just slap some stuff together and if it works at all, it's good enough -- it's very hard to find someone with good training and experience who is willing to read and follow regulations and procedures (like correct HVAC duct design and construction or furnace installation and tuning manuals).

 

Cutting a hole in the return near the furnace is absolutely the WRONG thing to do for the reason you mentioned.
There's nothing wrong with flex duct IF it is installed right. I know what you mean about trying to find someone to do the job right. That problem seems to be widespread especially with oil fired equipment.

I do believe you are on the right track in insisting on a proper duct system.

 

I just learned that this furnace has multiple fan speeds. According to the documentation I have, the air handler can move 2360 CFM at its highest speed and 1470 CFM at the lowest. I assume this is done so that the furnace can be used in a wider range of applications. I'm wondering if the fan was originally on a lower speed before the tech came to do the annual service on the furnace, and he set it on a higher speed while he was working on the unit. That would increase the CFM the fan is circulating, and if the return duct system was barely adequate for the slower speed, it would definitely be inadequate for the fan running at a higher speed, leading to the situation we're in now.

Does this make sense, or am I way offbase?

 

Fan speed for heat is normally low but can be increased if the temperature rise is too high. The spec'd temp rise should be on the furnace data plate or in the installation manual. Rule of thumb for an oil fired furnace is 60-80*. If you don't know how to measure temp rise, post back for instructions.