Knight inducer fan keeps failing

EdFerris

I've had to replace the inducer fan (FAN3033, 100145006) twice in the past four years for rough bearings.  What could be causing this?  The unit (KBN286) works fine until it locks out because the fan won't start.  On removing the fan it has a rough spot it won't freely turn past.  One season I had the intake open from the side of the unit, so it's not getting bad draft.  The local Lochinvar experts say they don't have problems with the fans.  All I can think of is bad bearings from the factory, though.

The local motor shop won't try rebuilding it.  So I have to spend $750 to replace the whole fan.  Do you know anybody who can just replace the bearing, instead?

EdTheHeaterMan

Inducer fans are an interesting component. First of all, they are moving exhaust gasses, and when you take them part and try to put them back together, there is the possibility that a seal or gasket may fail, Then you can get Carbon Monoxide to pass thru the compromised seal. No motor repair shop wants to deal with that. The seal where the shaft from the motor enters the squirrel cage fan housing can also be compromised. Then there is the fact that the fan is dealing with higher temperatures, and corrosive exhaust gasses, so the way that the fan is attached to the shaft is better left to the manufacturer.

In the 1980s when the forced draft fans were introduced, the motor repair shops found out that their insurance rates would go up if they did repairs on combustion fan motors and they failed after the rebuild. So they stopped that practice.

Jamie Hall

I hate to say this, but if you are having chronic trouble with a component -- such as that fan -- and others don't seem to, is there anything about the maintenance or installation of the fan which might be problematic? Do the bearings need lubrication? Is the installation such that moisture can drip onto the shaft? Is the installation such that the airflow is unbalanced? Lots of things to look at...

EdFerris

Do the bearings need lubrication?  There's nothing about it in the Knight manual or installation instructions for the replacement fan.  I don't see any oil ports.  And I would expect sealed ball bearings on this motor.  The faulty fan feels like it has a bad ball bearing, not the scrape you get from a bronze bushing, and it did not make a screeching noise.  However, if the motor does run in bushings, they have never been oiled, so you'd expect them to fail.  Does anybody know if this fan has them?

The airflow is not obstructed as far as I can tell.  As I said, it was running with an open intake for one season.

EdFerris

Since the fan is upstream of the burner, it does not get hot or deal with exhaust gases.  The impeller is plastic and not at all melted.  Perhaps the motor shop hasn't noticed this.

hot_rod

Here is the fan on a smaller Knight. It pulls intake air and a gas mix from a negative pressure gas valve, pushes into the combustion chamber. They run a bit warmer than the boiler temperature on the aluminum housing.

It sounds like a bad bearing, if it is pulling in clean fresh air?

pedmec

You need to make sure that you are not recirculating gases or moist air. i have taken a lot of these blowers apart and what i have found is that moisture is getting into the combustion air intake and causing the bearing failure or the logic controller is damaged. you can see signs of of moisture getting slung to the motor wheel housing. most failures that i have seen have the combustion air tied directly into the venturi's. a leak under the cover from condensate drainage will cause this too as it will suck up the moisture.

EBEBRATT-Ed

I think what @pedmec posted would be what I would look at.

@EdFerris

Since you have replaced it previously can it be cut apart to see what failed or send it back to Lochinvar to let them investigate.

All MFGs say "it never happened before you're the first one"

EdFerris

Here's the last bad one on the bench and the current one in use.  You see that it is mounted on rubber isolation and the plastic centrifugal impeller is in an aluminum housing.  The housing is cold in use, so none of the combustion heat is getting to the motor, which vibrates noticeably.  There is no reason it should not run perfectly smoothly.

Jamie Hall

As has been suggested, return the bad unit to the manufacturer, using the distributor who supplied you (don't do it yourself, unless you are the distributor) with details of the installation. If you are losing units regularly, something is making that happen, and it would be to everyone's benefit to find out what. Just attributing it to bad karma for your units isn't going to help.

EdTheHeaterMan

I see that is a variable speed EMC motor. I am familiar with that type of combustion air fan. It operates a special type of gas valve that depends on the amount of suction provided by the fan to draw the proper amount of gas from the valve. That is how the variable input happens on that type of equipment. My reference to the fans that are located on the exhaust side was premature. However the same issues with motor rebuilders apply. You see that fan contains not only combustion air, but it also contains the fuel. If a leak in a seal or gasket were to happen as a result of rebuilding that motor, there could be a gas leak into the space around the boiler. Then leaking gas into the boiler room could be considered a little dangerous if there happen to be a spark from a relay or light switch in that room.

You will not find a motor shop that is willing to rebuild them for pretty much the same reasons I stated above. just substitute a raw fuel leak for Carbon Monoxide from above.

EdFerris

Aha!  Moisture in the intake!  The original installer put the exhaust pipe just West of the intake, so a cloud of condensate is getting sucked in most of the time, when the wind is from the West.  So the bearing under the impeller is getting wet and failing.

I'll return it through F. W. Webb to Lochinvar with that explanation.

Thanks, @pedmec!

Ed Young is right about the gas leak possibility.  I won't mess with it.

EdTheHeaterMan

I wonder if that problem is a known defect? Looks like the FAN3033 has been discontinued by the manufacturer. The replacement is part number 100145006 and the OP is correct, It ain't cheep! I wonder if the replacement 100145006 has a change that solves the problem? The part was discontinued in 2019. When was the part for your boiler manufactured? Could you have received the original FAN3033 "problem part" form previous stock before the replacement 100145006 became available?

What part number is on your second part? 100145006 or FAN3033?

EdFerris

Both replacements have both part numbers on the sticker.  I think the numeric one is the AO Smith number.  Perhaps they're using the same fan and getting it from Lochinvar.  The sticker on the newer motor says "ENHANCED VERSION".

The part was discontinued, I think, when the Knight series changed to a fire tube design several years ago.  I know you can't get the KBN new.

ScottSecor

@EdFerris I believe AOSmith is the parent company of Lochinvar.

Jamie Hall

EdFerris said:

Aha!  Moisture in the intake!  The original installer put the exhaust pipe just West of the intake, so a cloud of condensate is getting sucked in most of the time, when the wind is from the West.  So the bearing under the impeller is getting wet and failing.

I'll return it through F. W. Webb to Lochinvar with that explanation.

Thanks, @pedmec!

Ed Young is right about the gas leak possibility.  I won't mess with it.

That is exactly what I was concerned about... don't kill the messenger!

GGross

@EdFerris If what you say is the case, it is not so much the moisture in the intake that is the issue, rather what is in that particular moisture. It is sucking in the flue gas, that will destroy just about anything given enough concentration and time. A little water won't really hurt it unless it hits electronics, Flue gas on the other hand will eat right through several components in that blower, and other things in the cabinet. If it has a venturi attached to the gas valve, that will be the next component to fail, and this will keep happening until the flue stops coming back into the intake

EdFerris

For now, I've disconnected the intake pipe, so the unit is drawing air from the basement.  We'll see how long the fan lasts - it is already vibrating.  Is there any downside to using inside air for the intake?  I would think that having the intake and exhaust on opposite sides of the house, or at least a good distance apart, would be better than the common practice of putting them next to each other.

GGross

EdFerris said:

For now, I've disconnected the intake pipe, so the unit is drawing air from the basement.  We'll see how long the fan lasts - it is already vibrating.  Is there any downside to using inside air for the intake?  I would think that having the intake and exhaust on opposite sides of the house, or at least a good distance apart, would be better than the common practice of putting them next to each other.

Drawing from inside the house just be careful there isnt a gas water heater or some other appliance near it, or it could pull the flue from that backwards, keep the area clean, no chemicals or paint or anything weird near the unit. This should be the case anyway, but usually people start storing all the stuff like that near the boiler after the installers leave. Some manufacturers have rules regarding opposite sides of the house etc. I know many brands that allow it, but people usually just want one hole cut so they put them right next to each other. Flue gas recirculation is the most common issue I see in my area, I tell everyone about the downfalls of it, and they still install them so they recirc.

hot_rod

I see some of the mod con brands are offering intake air filters. Id add one for either outside or inside air

You have a high powered vacuum cleaner essentially.

Pollen, dust, grass clippings, lightning bugs, anything within inches of the intake air opening can get sucked in.

I separate the intake and exhaust by as much as the manual allows

I suspect concentric vents shorten the life of many condensing boiler components also

EBEBRATT-Ed

most mod cons they want the intake air and the exhaust to be in the same pressure area that is why they locate them together

hot_rod

EBEBRATT-Ed said:

most mod cons they want the intake air and the exhaust to be in the same pressure area that is why they locate them together

I have read that for years, not sure what it means or how you would measure that. My boiler is in the corner of the shop, so I took exhaust out one wall, intake around the corner. About the same distance from the ground if that counts as the same pressure area?

I like to see all appliance vents out the roof if it can be done. Noise, steam, etc disappears and doesn't bother a close by neighbor. Two separate pipes 24" or so apart, exhaust up a bit higher.

Near the roof peak if you are in snow country.

PC7060

hot_rod said:

I have read that for years, not sure what it means or how you would measure that. My boiler is in the corner of the shop, so I took exhaust out one wall, intake around the corner.

Same here. 

Jamie Hall

The idea of having the intake and exhaust in the same pressure zone is simple -- that keeps the external draught pressure differential between the intake and exhaust constant, so that the draught settings on the burner stay constant.

One of the more subtle aspects of building engineering -- but one which sometimes gets overlooked (the John Hancock building in Boston being the poster child) is aerodynamic effects anywhere there is a corner -- either an inside corner or an outside corner. It can be vertical, like two walls, or horizontal, like a wall and a roof or even two sides of a roof. Any time the wind blows, even a breeze, there can be quite a pressure difference between the two surfaces -- and on either surface, quite a substantial pressure gradient as you go along the surface in the direction of the air flow.

evp

I’ve replaced 4 of these fans in the last 6 years on a lochinvar KHN199. Three of them had the plastic fan blade disintegrate and the latest one just died. There is obviously a poor design element of the fan or the way it integrates with the boiler. I should have kept my old cast iron boiler. It was bomb proof. The small improvement in efficiency- really only about 10% in real world use, the numbers the manufacturers state are from a lab under ideal conditions. Don’t believe the sales hype of degradation in cast iron boilers and the huge improvement in combustion boilers. The small savings is offset by the high cost of maintenance and a more complex system.

pedmec

@evp you need to check your venting. You need to stop blaming the product. its a bad habit that prevents anybody from truly solving the problem. To think that a major manufacturer would keep on selling a product that fails as much as you have is beyond belief. I work and install lochinvars all the time and have not seen this happen.

What I have done is opened the motor housing up on the failed ECM and check to see if flue gas and moisture is getting in the air intake. you should see stains on the inside indicating flue gas are getting sucked in. if you remove the top cover on the boiler, inspect the PVC attached to the air intake. There will be a hole in the bottom of the PVC. this allows any moisture that forms in the air intake to drain. sometimes installers move it and the hole is not on the bottom. If its installed correctly and draining then your getting flue gas recirculation and the condensate can also get sucked into the motor electronics by the little cooling fan in the rear of the motor.