King 5502M exhaust fan (USSC) (2024)

Hello,
We have a 5502M coming on for it's fourth year of operation.

We put it through the self-test and the exhaust fan is not working properly. It's supposed to turn on full and then reduce to a level just above the minimum pressure switch setting according to the manual.

Instead of turning on full, it tries to spin up (we have the panel off on the right-hand side as you look so I can see it moving a bit) and gets to what I guess would be about 1/10th of what it should be before spinning down and trying again. This repeats every two seconds or so until I move on to the next test.

Any idea what this could be? I took the fan off and cleaned out the ash/soot from inside the housing and the fan spins freely when pushed by hand if that makes a difference.

I'm by no means an electrical expert but I do have a multimeter so can I remove the fan and test whether the connectors are receiving the right power from the control board? Or is this likely to be something else entirely?

Thanks for reading

A little update...
I took the exhaust fan off and hooked it up directly to a power source and it came on full so I think that eliminates it as a problem.

I switched the pellet stove on and all was working OK. The exhaust fan appeared to running full and the pellets ignited but as soon as the room fan came on, the exhaust fan returned to ramping up for a second and then dropping back. I tried changing the exhaust fan from auto to manual and I do hear a little increase in fan power as I cycle up through the levels but it always drops back to nothing within a couple of seconds.

Eventually, the burn pot flame burned out.

One thing I forgot to say was I took the vent pipe off a week ago to give it a good clean. Is it possible that a leak somewhere there could cause this behavior or am I looking at a new control board. Please say it's something a little cheaper

Ssyko said:

it sounds to me that the combustion blower motor is getting warm and either starting to seize or on the verge of thermal shut down. test your motor again with its own power cord plugged in to the wall outlet and let it run for half an hour or so and see if it slows down.

Click to expand...

Thanks for responding.
I know it's not 30 minutes, but I did run the motor directly via a power cord into the wall outlet for 2 or 3 minutes and it seemed to be steady at full speed with no problems. It's only on the self-test (which I run when the stove has been off for at least 12 hours) where it sounds like it gets sent the signal to ramp up, then I hear a click and it powers down, then it tries to ramp up again and this 'ramp-up; click; power-down' process repeats until I tell it move on to the next test. I probably let it try for 4 or 5 minutes in the hope of seeing an error code but got nothing.

This is test #1. I'm a bit confused by what part of it means
1. Exhaust Fan Output Test – The display will show “drft”. The exhaust fan is turned on full then reduced to a level
just above the typical minimum pressure switch setting. The ON LED indicates whether the pressure sensor
is detected. If the pressure switch is not detected, the fan ramps to full on for two seconds then returns to
the previously established level if the pressure switch closes. If the Draft Fan Fuse is not blown and the fuse
detection circuit is functioning, the Draft Fan LED will be lit and the other three top row LEDs will be off.

I'm reading this to mean it's testing that the exhaust fan works *and* that there's no pressure sensor issue. Do you think a pressure sensor issue could cause this kind of issue on a self-test?

Connecticut Yankee said:

I would suggest doing the full 30-minute test that Ssyko recommended. He's one of the experts on this forum, and well worth listening to. If you follow his advice, you are likely to learn something useful, whatever happens.

Click to expand...

30 minute test and oil the bearings... 4 years, you have bone dry bearings, surprised it even turns at all.

Connecticut Yankee said:

I would suggest doing the full 30-minute test that Ssyko recommended. He's one of the experts on this forum, and well worth listening to. If you follow his advice, you are likely to learn something useful, whatever happens.

Click to expand...

I disconnected the fan and ran it directly to the wall outlet for 30 minutes and it stayed on full with no issues. At the same time, I put the stove into diag mode and checked the voltage going to the fan and it was a constant123/124 volts.

One thing I did notice is that if I open the stove door during the self-test, the fan ramps up to full so I guess that means the vacuum switch is good.

I've never had anything hooked up to the fresh-air intake pipe (manual said it was optional) but I did put a long thin pipe in there to make sure there were no blockages and I saw it reach the burn pot so I assume all is good there too.

Is it a terrible idea to hook a desk fan up and point it at the air intake to see if that keeps the thing running?

olivercfc said:

Is it a terrible idea to hook a desk fan up and point it at the air intake to see if that keeps the thing running?

Click to expand...

Change from a negative pressure to a positive pressure stove!
not my idea of a good move. Can we say smoke leak?

johneh said:

Change from a negative pressure to a positive pressure stove!
not my idea of a good move. Can we say smoke leak?

Click to expand...

Glad I asked
Now I know what that whole negative/positive pressure thing means.

When you say smoke leak, would it be to the point where I smell it in the house before the pot burns out? As I said in the second post I removed all the vent piping to clean it prior to the problem (I tested it the day before with a real overnight run, When it failed to burn properly afterwards was when I started to get into the diags.)

In looking again, it's possible the vent pipe isn't seated on the stove properly because the outdoor horizontal pipe is not at a 90 degree angle so I'll be re-doing that today. The stove is positioned in a corner so there's a bend to get it through the wall and I kind of have to push the stove on to the pipe and not vice-versa.

The last time I ran it (with the problem) the exhaust fan came on full until the room fan started and then it pulsed until the pot flame died. That room fan is *loud* so maybe that's just how the exhaust fan works and I didn't notice it before.

I'll re-do the vent piping and report back.

SidecarFlip said:

+1. Very bad idea and a great way to burn your house down.

Click to expand...

Oof... thanks for confirming

Ssyko said:

Try resetting the control to factory settings. To return the control to its original factory default settings, press and hold the AUX UP and AUX DOWN buttons together for three seconds. When it is done give it a try.

Click to expand...

Tried that yesterday.
I'd left the stove door open after putting the thin pipe through the fresh-air inlet and tried the diags again. When I went into diag mode I got 'err 9'
Then I realised the door was open so I closed it, did the reset (twice, both times 'BYE' appeared) and the err 9 went away but the diags performed as they had been doing.

olivercfc said:

The last time I ran it (with the problem) the exhaust fan came on full until the room fan started and then it pulsed until the pot flame died

Click to expand...

Check the connections on the White wire attached to the exhaust fan and room fan, also inspect the white wire for shorts or pinched wire.

SidecarFlip said:

You need to check the continuity of the upper limit snap disc (on the stop side of the firebox) as well.

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Does the 5502 have a high limit switch, I thought it ran off a Thermistor attached around the exhaust fan, but I could be wrong.

Not sure, I only am familiar with the 6039's and 41's. However, there is no polarity on any of the component leads as the supplied current is ac. Motor speed relative to settings is accomplished by electronic chopping of the voltage, not the frequency.

Made a mistake... the board chops the frequency, not the voltage. Basically a small Variac which is why they use shaded pole (induction-repulsion) motors. They draw little amperage. and the rotational speed can be easily controlled. Besides, they are inexpensive and really have no moving parts other than the armature but the downside is not much start torque which, is why maintaining the bearings is important.

SidecarFlip said:

However, there is no polarity on any of the component leads as the supplied current is ac. Motor speed relative to settings is accomplished by electronic chopping of the voltage, not the frequency.

Click to expand...

The Auger, Hopper switch, Room blower and the Exhaust blower all share the White/neutral lead, so could a intermittent short in any of these components or the wire could make the exhaust blower malfunction?

ARC said:

The Auger, Hopper switch, Room blower and the Exhaust blower all share the White/neutral lead, so could a intermittent short in any of these components or the wire could make the exhaust blower malfunction?

Click to expand...

Anything is possible with an older unit. I believe I'd first check the continuity of all the wires with a multimeter.

SidecarFlip said:

What are 'diags' anyway? The board resets to factory parameters (algorithms ), the firmware version flashes and the word 'BYE' flashes on the readout. I suspect the board you have installed is the incorrect one.... Is it a 4 button (8 touch pad positions) or a 2 button (4 touchpad positions) board?

Click to expand...

I may not have been clear...
When I say "diags" I mean I held the "OFF + AUGR" buttons for 3 seconds and ran through the 9 different tests

I ran diags, then did the reset (AUX UP + AUX DOWN) - then ran the diags again

My control board has a 4 char display at the top, then "HEAT RANGE (up/down) | ROOM FAN (up/down) | DRAFT FAN (up/down) | AUX (up/down)
Then four more buttons: ON | OFF | AUGER DELAY | MODE (auto/manual)

ARC said:

Did you check the vacuum switch hose for cracks or plugged with soot. I would try to jump the Vacuum pressure switch to see if vacuum or vacuum switch is the problem.

Click to expand...

Yeah, a couple of weeks ago when the problem started we suspected this. While checking, the pipe seemed a little brittle and then the P2 (positive) connector snapped off. We got a new one and and installed it.

It's probably still worth checking while jumping the switch I guess. Do I just join the two connectors that connect to the round pressure switch? Do I need a car-type fuse in there or anything?

After re-sealing all the pipes, I had slightly different results.
As usual, after switching on, the fan was on full and the burn pot started filling with pellets, then it ignited. But the room fan didn't come up and the "DRAFT FAN" light was flashing every 2 seconds or so.
According to the manual:

This indicates that the stove is in normal operation and that the vacuum sensor detects a loss of pressure either because the door is open or because there is negative pressure in the room with respect to the exhaust.

We replaced the door gasket and it passes the paper test so I guess it has to be the negative pressure thing.

One thing I noticed with the exhaust fan (when I removed it to plug it directly into the wall outlet) is the gasket looked very worn so I bought some Permatex High Temp gasket maker but haven't tried that yet.

I was reading the causes for a vacuum issue and it says to clean everything. I have already done all the suggested cleaning except for the "brass port inside firepot" (it says it could be clogged)... is that the little hole next to the air intake hole? It's listed as the 'igniter tube' in the parts guide but I don't have a problem igniting