King 5502M - hopper fire (2024)

I have a King 5502M pellet stove that heats an outbuilding. Last night it lighted as normal but this morning the flame was huge and the room fan was no longer blowing. I looked in the hopper and the underside of the lid is burned while the pellets at the top are singed. The ones at the bottom are blackened/burned so I'm reasonably confident there was a hopper fire.

Is the room fan not blowing a cause or symptom?

And shouldn't it shut down if it detects a fan not blowing?

Still need to do a proper inspection/test on it but wanted some advice first. Thanks.

Mt Bob said:

Your combustion fan was not running,for some reason. A power outage, fan motor quit,or control board quit sending voltage to the fan motor. Looks like the hopper lid did it's job, and contained the fire.

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Thanks for the response.
Looks like I can plug the fan directly into the mains to test so I'll do that tomorrow. Seems like that would be cheaper than the control board.

Here's the lid if anyone is interested.

olivercfc said:

And shouldn't it shut down if it detects a fan not blowing?

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Yes if exhaust blower not working stove should shut down with loss of vacuum. Without room fan stove should overheat and shut down. Did you lose power? How is your venting set up, did you have High winds that could have blown back into your vent pipe? In order for fire to reach the hopper it had to go up chute then down auger quick enough to not be pushed out into chute. The auger/chute design was suppose to eleminate hopper fires that direct to firepot auger system sometimes allowed. Are your pellets extremely long? Could they have bridged the chute causing a plug-age that then caught on fire? Another possibility is the triac on the control panel for the auger went bad, stove shut off but the auger continued to run because the triac was stuck in on position over filling burn pot creating huge flames.

ARC said:

Yes if exhaust blower not working stove should shut down with loss of vacuum. Without room fan stove should overheat and shut down. Did you lose power? How is your venting set up, did you have High winds that could have blown back into your vent pipe? In order for fire to reach the hopper it had to go up chute then down auger quick enough to not be pushed out into chute. The auger/chute design was suppose to eleminate hopper fires that direct to firepot auger system sometimes allowed. Are your pellets extremely long? Could they have bridged the chute causing a plug-age that then caught on fire? Another possibility is the triac on the control panel for the auger went bad, stove shut off but the auger continued to run because the triac was stuck in on position over filling burn pot creating huge flames.

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I've lost power once before with the stove running and it stayed shut down when power returned. That outage was for at least 1 hour though. This time, the control board looked like it was running normally but the room fan was not blowing.
Not sure what would happen if it was down for a few seconds or so.... so I don't *think* I lost power but it's not impossible. Maybe the control board got in a weird state after a few surges or something

The pellets don't seem any longer than previous years but I did notice that one particular brand was a bit more dusty than usual.

edit - forgot to mention the venting
There's about 2' horizontal straight from the back of the stove through the exterior wall and then 3' up. Very simple L-shape - since this is an outbuilding I could place the stove where I wanted with the easiest venting. No high winds.

After you get it cleaned up it will be interesting to see what happens in test mode;

This test is used at the factory where the stoves are assembled to test the functionality of the control and the stove
before the unit is shipped. To perform this test, press and hold the OFF and AUGER DELAY buttons simultaneously for
3 seconds. To advance through the test, press any key unless otherwise noted in the test step.
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.
2. Room Fan Output Test - The display will show “rfan”. The room fan is turned on full. If the Room Fan Fuse is not
blown and the fuse detection circuit is functioning, the Room Fan LED will be lit and the other three top row LEDs
will be off.
3. Ignitor Output Test - The display will show “ignt”. The ignitor motor is turned on full. If the Ignitor (AUX) Fuse is not
blown and the fuse detection circuit is functioning, the Aux LED will be lit and the other three top row LEDs will be off.
4. Auger Output Test - The display will show “augr”. The auger motor is turned on full. If the Auger Fuse is not blown
and the fuse detection circuit is functioning, the Heat Range LED will be lit and the other three top row LEDs will be off.
5. Hopper Switch Test – The display will show “hppr”. The “ON” LED is lit. If the hopper switch is open (lid is open),
the “HEAT RANGE” LED will turn on. If the lid is closed, the “HEAT RANGE” LED will be off.
6. Thermostat Input Test – The display will show “stat”. If the thermostat input is closed, the ON LED will turn on,
otherwise it will be off.
7. Flue gas Thermistor Test – The display will show the flue gas temperature in degrees F.
8. AC Frequency Test - Displays the measured AC Frequency in hertz (59-60) followed by the letter ‘H’.
9. Watchdog Reset – The watchdog timer is tested to ensure that the board can be reset. The message “BYE” is
displayed until the watchdog resets the board.

ARC said:

After you get it cleaned up it will be interesting to see what happens in test mode;

2. Room Fan Output Test - The display will show “rfan”. The room fan is turned on full. If the Room Fan Fuse is not
blown and the fuse detection circuit is functioning, the Room Fan LED will be lit and the other three top row LEDs
will be off.

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Well... this has confused me more. The self test didn't give any failure message or error for #2 but the fan didn't come on, it just sounded like electrical noise or like something was physically stopping the fan from moving. Problem solved I thought - replace the fan.
I took the fan out, cleaned it up a bit and hooked it directly to the 120v to double-check and it spun right up. I put it back in the stove and the control board gave an "Err 9" (which I think means controller error.) I unplugged it and plugged it back in and it passed the diag test.

I suspect this means the control board is on the way out?

piaman15 said:

hello. how did you make out? i have a piazzetta monia. the gasket at the end of the pellet feed was faulty and the hopper started to fire. i caught it early. there is no damage. the display shows e3 (high hopper temperature) now and the stove won’t start. i tried to reset factory settings. do i need a boot loader? i’m having trouble getting a dealer to help. i live in northern catskill mountains of new york state.

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You should start a new thread, instead of tacking on an old thread, about a stove that is nothing like yours.

Mt Bob said:

You should start a new thread, instead of tacking on an old thread, about a stove that is nothing like yours.

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ok, thanks for tip