suburban sf 42 furnace noise

Sounds like fan blower wheel rubbing due to expansion when furnace gets hot.

You will need to disassemble furnace and check for rub marks....motor drives two blowers. One side is combustion wheel and other side is room blower.
Either one could be loose, metal could be warping, motor could be loose/mounted crooked.

Once it starts the noise, let it run for 5 minutes, then shut the LP supply off at the tank. That will kill the Flame and the Furnace should run for at least 2 to 5 minutes before it shuts down. Observe if the NOISE quits the minute the flame goes out. I bet it will. It can be a burner orifice or a burner. If it is a blower wheel or motor problem the noise will continue when the flame goes out as the system will still be hot. Doug

From Suburban.

A SF20-25 could make that noise if the restrictor at the throat of the burner had a gap around the perimeter. Doug

Thanks for all your help I will test it tomorrow. I'm almost positive its the burner. It only seems to squeal when the flame is lit.
Looks like I will be taking it apart either way.:(

Also from Suburban for your model. Doug

Check the burner alignment and physical integrity (is it cracked or does it show signs of swollen areas), the position of the secondary air plates around the neck of the burner, the position of the curved air shield next to the orifice, and do a visual inspection of the combustion air wheel.

ok so I ran the test this morning with the burner lit and the noise being produced. When I shut off the valve the noise stopped instantly. I ran it for about 10 minutes every time the burner is lit for the first 15 seconds it will produce that noise.

Ok so I have taken the unit apart. Here is what I have

No luck! I took everything apart cleaned, checked and reassembled but it's still making the now dreaded noise. Not sure if I should start throwing parts at it or bite the bullet and buy a new one. Oh and while working on it I found out it's not a sf42 but a sf25.

surf bum wrote:
No luck! I took everything apart cleaned, checked and reassembled but it's still making the now dreaded noise. Not sure if I should start throwing parts at it or bite the bullet and buy a new one. Oh and while working on it I found out it's not a sf42 but a sf25.

Just get a new burner. That is the first part to replace. Doug

Ok I got the new burner, everything is the same except a reducing ring on the inside(see pics). Should I grind this ring out and make it like the older burner or leave it alone.

OLD


New


Both


Thank chris