Ravelli Francesca - Auger Fire!!!

[followyourbliss]

I purchased a Francesca 2015 used. I had it thoroughly cleaned before use including the hopper and behind the blast doors. I had noticed the pellets will overfill the pot, so I turned the pellet percentage to -5 (as low as it would go). Last night I cleaned it and started the stove per usual. This morning when I woke up, the stove was on but the flame was gone. I could hear the auger was binding. The stove was still in "work" status and still warm, so I set it to "final cleaning" (shutdown) mode. A few minutes later I smelled burning rubber. There was smoke coming from the top of the stove.

I unplugged the stove and took off the right side cover and saw fire from the junction of the auger chute at the back of the firebox. I extinguished the fire and noticed it was still very hot and the firebox was filling with smoke. I plugged it back in to try and let it go through the shutdown phase. Fire was blowing out of the auger chute at which point I unplugged it again and emptied the pellet hopper. There were lit pellets dropping into the hopper from the auger chute. I extinguished those as well. It took nearly 30 minutes for the auger chute to cool down.

I've started pulling the stove apart, the auger is burnt looking (blued), and the chute was packed with burned pellets.
I’m sure this is a very unusual occurrence. The only good thing in all of this is that I was awake when it burned rather than asleep, or most likely the house may have burned down.

Has anyone heard of or had this experience, and why on earth would the auger chute catch fire? I'm guessing the "rubber" seal in the auger chute burning caused the pellets to continue burning back to the hopper. I'm obviously concerned this could burn down the house next time.

Thank you in advance

 

[Pelleting In NJ]

I think the root cause of the auger shoot fire is that the stove overfeeds pellets, which then eventually back-up the chute, allowing the firepot flame to move up the chute to the auger.

The backup is because
- the pellets burn too slow in the burnpot (are they damp? or way too little combustion air?),
- or there is a problem with the control board (turning on the auger motor with too-long of an ON time). Normally, the auger is only turned ON for a second or two, between an OFF time of about 7 seconds. Does your auger run continuously?
- or the previous owner replaced the auger motor with a faster speed. The Ravellis typically use a 2RPM clockwise motor.

 

[johneh]

The main cause of an auger fire is a dirty stove
most likely the path from the firebox to the
chimney. Not enough air to burn all the pellets
being dropped/pushed into the burn pot.
Fire burns back up auger shoot looking for air
Tear it down clean every sq. inch of ash
out of the stove /chimney

 

[followyourbliss]

The auger motor is a 2015 date code with Ravelli label. 2rpm.
I hear it cycle like it should, doesn't run constantly.
I reset to factory settings, set the auger percentage to the lowest setting and the air speed to the highest percentage. Still seemed to be loading too quickly for the air speed.

 

[Pelleting In NJ]

Have you pulled the combustion blower motor off the housing, to clean inside? There are six (I think) philips head screws that hold the motor to the housing, then it can be pulled out after you rotate it so the fan blades clear the housing.

 

[followyourbliss]

I will pull that out next.
I've got to pick up some high temp RTV. I also wanted to test the auger motor, but I'm not sure how. I remember on my old stove I could rotate it with plyers, but the gearing is so low it's not easy.

 

[Ssyko]

Don’t use pliers. Make a cord and plug it in the wall.

 

[johneh]

Don’t use pliers. Make a cord and plug it in the wall.

attach to the leads on the motor and see if it works

 

[followyourbliss]

I thought I'd be smart and run it off a battery charger thinking it was DC. Apparently not.

 

[SidecarFlip]

It's an induction-repulshion (shaded pole) ac motor, Line voltage only. I would also remove the dummy grill in the pellet hopper. It's worthless. I used mine for a campfire grill years ago. Good for grilling burgers and not much else.

Far as the auger goes, it's fine. If anything it might have gotten a bit case hardened.

haven't see a hopper fire in years (since positive draft stoves were basically outlawed.

Sounds to me like you venting system if filthy and the combustion blower plenum is full of ash too. Clean stove and clean venting is a happy stove and most issues arise from poor cleaning maintenance.

 

[followyourbliss]

Thank you for everyone's comments and help.
The blower was cakes with sooty ash. I thought I had cleaned that pretty well, but until I pulled it out and brushed the fins, I really hadn't gotten it all.
I pulled the auger screw apart as well and cleaned it thoroughly. It had a sticky coating from the fire which probably would have caused the pellets to stick a bit.
Good news is it's all back together and seems to be working fine. I left it off through the night for my wife's reassurance.
I do notice the glass gets some black soot on it. Thinking of combustion, sounds like it's running rich, but I'll watch that. I know you'll always get some of that.

Thank you again for all the help.

 

[SidecarFlip]

They all do that to a certain extent. The 'air wash' claim is a fantasy, perpetrated by the builders and stove salesmen. Easiest and quickest way to keep the view glass clean between stove cleanings is, open the door while it's running and take a small paintbrush and remove the soot / ash. Has to be a NATURAL BRISTLE paintbrush, not a synthetic one because the glass is hot and a synthetic one will melt. A natural bristle brush won't. I do that at least once a day between stove cleanings. On the combustion blower, never use anything but a paint brush on the fan. It's hard and brittle from the combustion heat and a sharp object like a putty knife will shatter it.

I dispensed with the 'gasket' years ago. I take and apply a small bead of RTV red high temp sealant to the flange on the motor side (not the plenum side) and let it sit and vulcanize and set for a day or two and then reinstall it. That way, the RTV seals it but you can get it apart easily when you clean it. I clean mine every spring when I tear mine completely apart and then I also service ALL the motor bearings too. 15 years+ and I've never replaced one motor driven component.

 

[followyourbliss]

I think the root cause of the auger shoot fire is that the stove overfeeds pellets, which then eventually back-up the chute, allowing the firepot flame to move up the chute to the auger.

The backup is because
- the pellets burn too slow in the burnpot (are they damp? or way too little combustion air?),
- or there is a problem with the control board (turning on the auger motor with too-long of an ON time). Normally, the auger is only turned ON for a second or two, between an OFF time of about 7 seconds. Does your auger run continuously?
- or the previous owner replaced the auger motor with a faster speed. The Ravellis typically use a 2RPM clockwise motor.

It still seems that the pot is filling too much with pellets. It's been running about 5 hours and the pellets are at the top of the pot.
I have the pellet ratio as low as I can set it and the air as high as I can set it.
Do you know how else I can slow the pellet feed down? Is there anything in the calibrations or even the climate comfort that effects this as well?

Thank you.

 

[Pelleting In NJ]

Is the flue pipe somehow restricted? Or alot of wind blow-back/backdraft?
Did you try another brand of pellets?
What does the flame look like when the stove is running?
Did you check if there are any restrictions in the air intake tube?

 

[Pelleting In NJ]

It could also be that some of the control operating parameters were incorrectly changed by someone, some of which control the pellet fuel feed rate. I will look back at my notes and post how to read and alter the operating parameters.

 

[followyourbliss]

The flue is clean. It's a 4" liner that was installed 5 years ago and cleaned just before installing this stove.
All the internal pipe is 3", brand new for this stove.
I've tried 3 brands of pellets, no distinguishable difference. Purchased indoors and stored indoors, so shouldn't be moisture issues.
Intake tube is clear. I don't have it plumbed. It's a drafty 1920 house and never had an issue with the last stove for the 5 years we ran it.
Flame and pot pictures attached.

 

[Pelleting In NJ]

That is bad...the burning pellets should only pile-up to maybe an inch from the bottom of the burn-pot.

 

[followyourbliss]

Yeah, that's after about 5 hours of burning at level 4.
I've shut it down and will clean it again. Not sure what's going on with it.

 

[followyourbliss]

Could a bad flowmeter (debimeter - 55255) cause this?
I'm assuming it would trip an error code (09) as well. I haven't seen this code at all.

 

[Pelleting In NJ]

I don't think it is the air flowmeter. I think either there is still some serious restriction of airflow thru the stove, or the pellet feed parameters of the control board, or the combustion fan speed parameters, are really off from what they should be. See page 6 of the "Rev2" RDS manual for how to get to the "Calibration" screen so that you can view the "Factory Settings". These settings are called "TF", which run from TF01 to TF54. Scroll thru the view factory settings, and write down the value of each TF parameter, then post to this forum and we can perhaps see if anything is wacky. See page 9 thru page 11 for the list of the TF parameters and what they do. If some of these are way off, I would suspect pellet feed rates TF16, TF19, TF22, TF25, TF28, or the exhaust combustion fan RPMs TF33, TF34, TF35, TF36, TF37. There are 5 values that correspond to the 5 "Power" levels of the stove.

Did you clean the heat exchanger-tube area at the top of the firebox, above the removable triangular flame-trap plate? The ash builds up around the perimeter of that square opening, use a plastic spackle/putty knife to get in there to dislodge the ash so your shop-vac can get it. See the bottom half of page 3 of the similar stove Maintenence Manual, for a picture of the Flame-Trap.

 

[SidecarFlip]

Only 3 things that I know of that will cause ANY pellet burner to do that (Picture), either insufficient combustion air or a restriction somewhere in the venting as in dirty or a dirty combustion fan plenum or fan wheel.

Heck, I can run my biomass stove wide open (up to 7.5 pounds of fuel per hour) and never experience a full burn pot. All I get is an eventually overheated stove (room air blower cannot keep up with the heat exchanger) and a high limit shutdown eventually.

 

[followyourbliss]

I went through all the settings, the are listed below:

TF1 Screw Ignition - 03,3 sec
TF2 Max Load Screw - 004 min
TF4 Preheating Candle - 160 sec
TF5 Delta Flame - 021 sec
TF6 Threshold Fan - 185 sec
TF7 Threshold Restart - 176 sec
TF8 Screw Start - 01,4 sec
TF9 Duration Start - 008 min

TF11 Screw Cleaning - 01,3 sec
TF12 Duration Cleaning - 015 sec
TF13 Frequency Cleaning - 030 min
TF14 Smokefan Cleaning - 2500 rpm
TF15 Threshold Off - 113 sec
TF16 Screw Power 1 - 01,1 sec
TF17 Flow Power 1 - 00,90 m/s
TF18 Speed Fan 1 - 085 V
TF19 Screw Power 2 - 01,6 sec

TF20 Flow Power 2 - 00,95 m/s
TF21 Speed Fan 2 - 090 V
TF22 Screw Power 3 - 02,1 sec
TF23 Flow Power 3 - 01,00 m/s
TF24 Speed Fan 3 - 095 V
TF25 Screw Power 4 - 02,6 sec
TF26 Flow Power 4 - 01,05 m/s
TF27 Speed Fan 4 - 100 V
TF28 Screw Power 5 - 03,1 sec
TF29 Flow Power 5 - 01,10 m/s

TF30 Speed Fan 5 - 112 V
TF31 Smoke speed ignition - 1500 rpm
TF32 Smoke Speed Start - 1500 rpm
TF33 Smoke Speed p1 - 1100 rpm
TF34 Smoke Speed p2 - 1200 rpm
TF35 Smoke Speed p3 - 1300 rpm
TF36 Smoke Speed p4 - 1400 rpm
TF37 Smoke Speed p5 - 1500 rpm
TF38 Altitude - 0000 m
TF39 Air Flow Meter - OFF

TF40 Recipe - OFF
TF41 Threshold no Pellet - 122
TF42 Maximum Threshold - 518
TF43 Delay Alarms - 060 sec
TF44 Black Out - 010 sec
TF45 Pre-ignition Block - 003 min
TF46 Min. temperat. Off - 004 min
TF47 Minimal Flow - 00,40 m/s
TF48 Max ignition Time - 018 min
TF49 Activate Candle - ON

TF50 Frequency - 60Hz
TF51 Degrees - F
TF52 User Draught - ON
TF53 Volt Max - 115
TF54 Service Hours - 2200

 

[Pelleting In NJ]

Nothing jumps out as unusual as far as your settings.
How did it look above the flametrap?

Maybe do a "leafblower" cleaning of the stove, outside. Disconnect the pressure switch hose before you do that, to prevent damaging the pressure switch.

 

[SidecarFlip]

I do that mid winter. Wife gets testy, I get the deck black as well as myself.