Burner Issue

Questions about repairs and parts for Nordyne furnaces, air conditioners and heat pumps for manufactured homes including Intertherm, Mac and Miller brands. Click here for Nordyne parts.

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jtmarten
Posts: 18
Joined: Mon Feb 04, 2013 4:34 pm

Tue Feb 05, 2013 7:40 pm

Hi
I have an issue with a Nordyne MGBB-090ABPQ-06. I had it serviced in Nov '11, replaced the burner assy and the pilot assy. The original burner assy was fine :evil: , just had a baaaad tech :evil: and a cracked pilot tube. He really just wanted to replace the furnace from the get-go. :evil:
Ever since he worked on it, I have a strong odor outside when the furnace is running, I'm guessing unburned propane. I get the odor once in a while in the house too.
I had a different HVAC tech look at it in Dec '12 because the blower was cycling badly: run for 10-20sec, shut off for 45-60sec, repeat. I replaced the fan switch, problem persisted. He checked everything out, and it was running too cool. His best guess was the valve was sticking and not allowing full gas flow. He checked the interior of the house while the furnace was running and found no increased CO2 levels. I verified this was to make sure the heat exchanger was still good. I swapped in the old burner, just to eliminate the new burner assy - it was not the problem. I replaced the valve (and newer burner assy), and no more cycling, seems to work just fine now; but I still have an odor outside while its running. The valve was properly set up; flipped the NAT/LP fitting so the LP arrow is facing the valve.
I just ordered a new #36 orifice, its the only thing I can think of that would cause too much propane to be flowing; can only guess the 1st tech messed with the orifice for some reason.
Maybe he installed a NatGas orifice?
It doesn't really appear inside like its running really rich either, the only yellow flame I get is right around the pilot assy, which the tech said is normal.
Any ideas?
Thanks!


DaleM
Posts: 385
Joined: Wed Apr 07, 2010 10:07 am

Thu Feb 07, 2013 10:34 pm

Not real familiar with that model, any chance you could post a pic of it? Has anyone checked gas pressure in and out of the control valve?

jtmarten
Posts: 18
Joined: Mon Feb 04, 2013 4:34 pm

Mon Feb 11, 2013 2:49 pm

I'll try to get a pic tonight. Its a non-computerized, 'dumb' furnace, circa ~1997. :lol:

I haven't had the in/out pressures checked. The last tech that looked at it did check the vacuum, it was running at 10.5". He said that was normal. I also need to check the voltage to the valve. The 1st tech repaired both wires that connect to it, just need to verify it is getting proper voltage.
I installed the new #36 orifice on Sat, looked to be the same size as the one that was installed.

The last couple days I'm seeing more yellow flame tops while the burner is on. We got the propane odor through the vents again this weekend, and this morning. I picked up a CO monitor last week, and it showed a max of 13 ppm, well under the 1st warning level of 70 ppm, so I think the heat exchanger is still good.

jtmarten
Posts: 18
Joined: Mon Feb 04, 2013 4:34 pm

Tue Feb 12, 2013 9:03 am

Image

Image

DaleM
Posts: 385
Joined: Wed Apr 07, 2010 10:07 am

Tue Feb 12, 2013 10:50 am

There cannot be any unburned propane coming out of the roof vent. Any propane that goes through that burner assembly will get used in the cumbustion process. As for the smell outside I suspect an ill burning flame. That is caused from a number of things or a combination of them: 1) the flow of propane into the burner is not correct, either too low or too high, need to test pressure into and out of the control valve. 2) the flow of intake air for combustion is too low, pull the combustion motor assembly and clean the blower wheel on it, clean the intake tube, (that's the 4" down tube on the right side of the unit). 3) there's a crack in the heat exchanger or holes in the exhaust tube leaking flue gases back into the fresh air intake pipe on the roof jack.

Your flame should be blue with yellow tips roughly about 2" high. You can watch it through the pilot observation door but you have to use a piece of glass to block off the opening. It has to be blocked to restrict any additional air into the combustion chamber while watching the flame.

As for the smell in the house, I'm leaning towards holes in the roof jack assembly. Once the blower comes on it can put enough suction pressure on that roof jack to allow it to leak flue gases. It then circulates them throughout your place and you get that smell. Put your CO detector in your duct at the register closest to the furnace, measure your ppm there. Should be ZERO.


jtmarten
Posts: 18
Joined: Mon Feb 04, 2013 4:34 pm

Thu Feb 14, 2013 10:42 am

Thanks for the help Dale! I'll check on these this weekend.

jtmarten
Posts: 18
Joined: Mon Feb 04, 2013 4:34 pm

Mon Feb 18, 2013 2:02 pm

I checked the voltage to the valve; 27.xx vAC. I pulled the inducer motor, the fan was pretty clean, no obstructions in the tube.
Have an appt scheduled for Thur afternoon to have a tech come look at it. :(

jtmarten
Posts: 18
Joined: Mon Feb 04, 2013 4:34 pm

Fri Feb 22, 2013 1:27 pm

OK. It appears the problem is in the ventilation. Was too icy/windy to let the tech on the roof to actually check the cap, but he said from the ground it appears rusty. Using his camera, there was too much soot to see if there were holes or cracks in the burner vent tube.
He said the flame appears to be choking. There is plenty of air being delivered by the inducer, but he thinks the air isn't fresh air, but mostly already-combusted air, causing the burner to run rich.
My options are replace the roof jack, or replace the entire furnace with either a standard or high efficiency unit.

I'm going to replace the furnace with a standard model, probably a Miller/Intertherm/Nordyne M1MB90.

If I replace just the roof jack, the furnace may run OK for a while, maybe a few years, but it is 16yrs old now. If I have it done by May 1st, I can use the standard 80% model. After that I'll have to go HE. Its a $1700 difference in price according to the first quote I received, so it makes sense to replace the system now.

1987Commodore
Posts: 383
Joined: Mon Oct 25, 2010 9:53 pm
Location: Steuben County, NY

Fri Feb 22, 2013 7:19 pm

I'd get a couple more quotes on the difference between standard and HE unit prices. When I switched, it made a huge difference in my (natural) gas bill.

DaleM
Posts: 385
Joined: Wed Apr 07, 2010 10:07 am

Sat Feb 23, 2013 5:22 pm

Good idea to replace the complete unit. It is probably sooted up inside the upper section of the heat exchanger. That is the first place that crap collects, impossible to clean out. Usually about clogged when the black soot starts showing up on the cap.

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