VC Defiant Encore - Air Intake Out of Control- Help!

[Free Monomoy]

Hi. Need some help here fellas. Been burning my 1986 VC Defiant Encore Cat Model 28 for a few years now very successfully. Did a partial rebuild this summer mainly to replace a damper tab. Did the cat while I had the stove pulled out as well as all backside gaskets. Inspected thermostat coil but opted not to replace as intake was fully open with cold stove and there were no signs of damage, I now question this decision.
Anyhow, as you probably know, when you put the back of the stove back on, the top and side are sealed with fiberglass gasket but the bottom has no rope, just gets cement. I sealed it with another tube of 2000 degree gasket cement. Put it all back together and did a cure burn to 500 degrees. no problems. A couple weeks in and 6-7 early season fires, I'm on the couch with my girl watching the Bruins game and the stove starts to fire up. Everything was on cruise control in cat mode at 450-500 exhaust baffle temp. Temp shoots up to 700 and I can see thru the box and into the exhaust outlet, looks like the refractory area is glowing red.....i cut off the air and am able to bring the stove slowly down and let it burn out the night with the lever/intake closed, an action that would normally snuff out the stove to the death.

I suspected the cement seal had given way allowing air to scream in. In retrospect, I am unsure. I pulled out the stove, pulled the back off again, cleaned out the old cement, and put it back in with a very healthy serving of Rutland black furnace cement via putty knife. I chose this after calling Rutland for their advice on which sealant would be best. Let it set up in place for 3-4 hours, put it back to the pipe and did another cure burn. Inspection yielded no other cracks or problems. All good. Until last night. Had a few nights normal burning and then last night, same failure, same temps shooting high, same visual of glowing red thru the exhaust as if Hell resided in the refractory system. Note that my refractory system has many cracks and some pieces of the ceramic have fallen apart. But this would not explain fresh air.

So Help me out before I rip it apart again.....My thoughts are: 1-Possible same gasket failure although I don't see how this could possibly be the case. 2-Some sort of refractory failure I am unfamiliar with but if so, how is the fresh getting in to fuel up the fire, did I mention I can hear it roar in? Or, 3-Could this possibly be a thermostat issue that is randomly opening the intake on a warm stove with even fire? Would this cause it to roar? 4-Something else????
What do you think...it's getting colder, times are tough, and I need this old baby to work for me. Thanks!

 

[Brian VT]

An easy check might be to hold a smoker (incense, punk) near there to see if it draws the smoke into the stove but probably not too easy when that puppy is at 700.

 

[cmonSTART]

Wow. Strange things happening there. Almost as strange as the Bruins being in first place

 

[homebrewz]

I have the same model stove, the 0028.

Are you sure that the lower side of the back needs to be cemented in? I believe there is a trough there that I thought was
some sort of air conduit.

I rebuilt mine also, and after I put it back together, I noticed I was having a hard time controlling the temp with the air flow.
By moving a smoking incense stick around, I was able to determine that some air was getting in on the back corners. I went along
those areas and carefully shoved some 1/4" gasket in the spaces along the back of the stove. It seemed to help. Part of it was
that I was also new to the stove and it can take cast iron longer to cool down than the steel stove I was using previously.

Perhaps the glowing you saw, was the cat lighting off and being reflected on the heat exchanger. Mine is doing that right now,
and the griddle is cruising around 650-675f (a little high in fact.. I just turned it down). I have seen the heat exchanger glow
due to the flame being directed directly on it, and I do my best to control that, but sometimes it happens.

 

[Free Monomoy]

Update: Thanks all for ideas. I chose to fire the stove tonight to see if the problem would happen right off the bat, plus it's starting to feel like winter outside. I'm 3 hours into the burn, rolling along around 450-500 in cat mode. As I suspected, the stove is burning normally. This leads me to think that the gaskets and seals are fine and the stove is mostly air tight. Although this is one step towards the solution in that I feel I can eliminate options, I'm still at a loss.

What do you all think or know about the thermostat coils and there behavior or likeliness to fail?

Any other thoughts that might cause erratic air flow or the sudden influx of air I seem to be getting. Hopefully she burns smoothly tonight, but for the first time in my stove heat life, I cannot leave her alone with true peace of mind. a real bummer.

Thanks

 

[homebrewz]

I suppose the secondary air shutter could be opening wider as the burn progresses. You can check to see if its cruded up
just be removing the cover, and the bolt that holds it on. It pierces the back of the refractory. The probe should be shiny clean
and the coil not full of fly ash and other debris.

It might just take a while to learn the operation of this stove. I like the stove, but its more complicated to run that it needs to be.

 

[Free Monomoy]

Been cruising now since last night without the issue reoccurring. I'm thinking it has something to do with the air shutter and perhaps the probe is failing intermittently.
If anyone has further comments on these probes and intakes, please write....

Homebrewz, just to respond to a few of your thoughts: Yes, I am sure the bottom of the back piece must be cemented in--I went over this repair in detail with a very reputable VC dealer. I can't imagine a cast to cast seal being air tight at all. You mention your griddle temp - As a convenience, I keep my thermometer (Rutland Classic), on the exhaust baffle. I have found it reads almost exactly the same temps as the griddle and personally I feel that the exhaust gas temp is a better reflection of what's actually going on in your stove. Also, this frees up the griddle for use and keeps the thermometer out of the way....while giving it a better viewing angle at the same time.
That said, I've got a few years on this stove now and feel I am one with it (most of the time), that's why this recent behavior was such a shock. I think you may be right and I will keep this diagnosis in mind. But I would disagree that it's a complicated stove....if it is, we make up for it with efficiency. I don't know anyone who burns less wood than I for the amount of heat I need each season.


Thanks & Cheers.

 

[homebrewz]

Well, I agree to disagree. I think these stoves, while certainly efficient, can be a bit touchy.
Btw, I run a thermometer on the griddle and the pipe.

Thats interesting about the back seal. Its not mentioned in the manual. When I was rebuilding
mine, I was told by someone on this forum to keep that channel open. I did notice some draw
in from the corners, but the extra gasket material stopped that. I did the yearly gasket replacement
on the moving parts a few months ago, and now its running really great.

 

[Free Monomoy]

Fair enough...
Now if someone gave you $2500 to go out and buy the stove of your choice, what would it be?

I'm now interested in this back panel/gasket cement thing. You could very well be right and I was misinformed. It just makes sense to me that that area should be sealed and that cast on cast would not be adequate. However, I could be wrong and I'd love to hear more about this from the folks with greater knowledge.

 

[homebrewz]

Fair enough...
Now if someone gave you $2500 to go out and buy the stove of your choice, what would it be?

I'm now interested in this back panel/gasket cement thing. You could very well be right and I was misinformed. It just makes sense to me that that area should be sealed and that cast on cast would not be adequate. However, I could be wrong and I'd love to hear more about this from the folks with greater knowledge.

Well, if I was building a house, I'd take that money and put a down payment on a masonry heater! I bought my #0028 not knowing much about stoves and just based on the good reputation of the older VC's. I didn't pay very much for it, but it needed a complete rebuild. Just to compare, I wouldn't mind trying something with non-cat secondary burn technology.

Yes, I'm interested in knowing what the factory's intent was for that back portion. If it does need a seal, I'll have to check mine out, but it seems to be doing well so far.

 

[phishheadmi]

Hey guys,

I've been learning a lot from the posts here on hearth.com and chiming in a bit here and there. I just finished re-building a Defiant Encore 2190 and while it's a bit different, I think it's mainly the same stove. I used the factory rebuild kit (fireback kit I think it's called) which comes with very good step by step instructions. While the instructions told me to clear the hardened cement out of the channel that the lower fireback sits in, it said nothing about replacing that cement or forming any sort of seal, so I did not. I replaced the secondary thermostat, on the back of the stove, but not the primary thermostat (which I'm having second thoughts about). I've not used this stove yet, so I'm not very familar with the operation. Does the primary air intake regulate itself, or does the shutter stay in one position once it's set? I'm assuming since there's a bimetal coil thermostat that this shutter moves and regulates the temp itself. I think I'm going to take the lower fireback and right side back out and replace the primary thermostat, at that time, should I seal the bottom channel of the lower fireback with cement? Any other pitfalls I should look out for?

 

[homebrewz]

There are instructions for replacing the firebacks in the manual, and at least on the #0028, there is no mention of sealing the lower portion with cement.
I would guess its the same for your stove, but you should check out the manual to be sure.

I'm not sure of the differences between the two models, but for what its worth... on mine:

The primary air control is controlled manually by the thermostat lever on the side of the stove. When I was rebuilding mine, I did take it apart to inspect it
and I was told by a professional that re-installing that coil was one of the hardest parts about rebuilding that stove. If I remember correctly, there is a trick
to it.. something about keeping pressure on the spring by winding it and pushing in as you tighten the set screw. If it seems to be working properly, you might
consider not taking it apart. The thing I would check is to see if the thin attachment cable is frayed or looks like its going to break anytime soon. It would be a
major inconvenience to have that thing break when the stove is back together.

The secondary air probe is controlled automatically by the bi-metal coil. It should be shiny and clean.

 

[phishheadmi]

Thanks homebrewz...

I didn't see mention in the manual about replacing the fireback, but I'll check again...I mainly went from the instructions that came with the kit.

Sounds like the primary air control is the exact same...maybe I won't screw with it right now...everything looks ok, including the cable. The only reason I thought about replacing the thermostat is because the guy I bought the stove from had a professional inspection and proposal of work that needed to be done...his proposal included the primary thermostat, but I'm 90% sure he didn't actually inspect the thermostat so maybe it's fine and he just figured for $60 he'd throw one in while it was apart...the same thing I was thinking before I learned what a pain in the neck it is. When my primary air shutter is fully open, the attachment cable is quite slack, is this the norm or should that coil be taking up the slack? The secondary probe is brand new so I know that's fine. I feel pretty good about the stove...$300 investment (includes the warming racks, shields, screen, tools, water boiler, all the matching goodies) for the stove and about another $700 in parts...saved about $500 in labor doing it myself and now have a beautiful like new stove for under a grand!

Thanks again...got a nice batch of porter coming out for this weather?

 

[homebrewz]

There should be some slack in the cable as I don't think you want it too tight. If its too tight, it might chafe against the stove and break. It should operate the primary air shudder efficiently, as in when the lever is pushed towards the front of the stove, the door should be open, and when moved the other direction, the door should be closed.

When I was putting mine back together, someone gave me instructions in a pm:
"There is a crimped stop on the rod that the friction spring stops against. On the other end of the rod a “T” bar is welded on. The T bar sits against the cover cap. The handle itself is what holds the rod to the right and provides the tension. Push the rod against the outside and tighten the set screw on the handle. There may be a washer used to help the spring stay aligned"

I just threw that in there in case you were wondering how it was put together. I believe there is only that spring on the t-stat. The bi-metal spring is located on the
secondary air intake probe.

Sounds like you got a similar deal.. I paid about the same for the stove and parts, but I didn't get the warming racks. You're ahead of the game!
It sounds like a nice stove.. congrats.

Yes, there is a keg of porter on tap in the basement! I'll be making some scottish ales soon, and then it will be lager season... all from scratch of course. Too cold to do ales in mid-winter.

 

[slindo]

Actually it isn't since you just run a coat hanger through so apart from having to let the stove cool, the time to replace the cable is trivial. Not like when I dropped the damper link down in between the inner and outer wall and hard to turn the stove on its side and shake it to get it out!

Re sealing the back, while it is not mentioned in the instructions, when I picked up my latest fireback kit the shop recommended doing so. However, I am not sure how important it is, since if it is leaking it will be dumping the excess air rignt into the rear box, where it will be immediately sucked up the chimney, and shouldn't effect the burn in any way. Or am I missing something?

The thing I would check is to see if the thin attachment cable is frayed or looks like its going to break anytime soon. It would be a
major inconvenience to have that thing break when the stove is back together.

 

[Tech Dude]

Check the secondary air probe. Likely the bimetal probe assembly is over-rotating on high temps and re-opening the secondary air shutter. Remove the cover and the probe with the one screw. If you remove the shutter, do not loose the shim ring on the screw. Inspect the probe for damage and if burnt off, replace it. Also ensure the door is flat. If warped, more secondary air will be introduced and an overfire may occur. You can inspect the assembly by having a fire with the secondary cover removed and heat shield (if present) propped out at the bottom. Do not remove completely as this will compromise your clearances.

 

[Free Monomoy]

Check the secondary air probe. Likely the bimetal probe assembly is over-rotating on high temps and re-opening the secondary air shutter. Remove the cover and the probe with the one screw. If you remove the shutter, do not loose the shim ring on the screw. Inspect the probe for damage and if burnt off, replace it. Also ensure the door is flat. If warped, more secondary air will be introduced and an overfire may occur. You can inspect the assembly by having a fire with the secondary cover removed and heat shield (if present) propped out at the bottom. Do not remove completely as this will compromise your clearances.

Update: Thursday Afternoon
Murphy's Law, the stove has been behaving well since the first post....been burning 24/7 since as well. This analysis sounds quite likely. I'm a little confused about the 'over-rotating' you mention but the concept makes complete sense. Also, the manually controlled intake is considered primary or secondary?
I guess i'll see how she goes and if it acts up again and warrants repair. I've got to pull the stove out to work on it so....if it ain't broke don't fix is the rule. we'll see. Thanks.

 

[Tech Dude]

The air control handle on the right side is the primary air. The bi metal secondary air control is at the back. It contols a small door that swigs closed at the cat heats up...if it ain't broke - don't fix it.

 

[phishheadmi]

I have another somewhat unrelated question...

I think I may have installed (I'm sure I'm messing up these part names, but hopefully you'll be able to decipher what I'm talking about) the damper activator link wrong (the hockey stick) to the damper handle. When I close the damper (engage the cat) it closes, but dosen't really "lock" into place...a light touch will open it. I fiddled around with it for a while and could only see two ways in which it could be connected...the other way definitely didn't work. My question is this...does that damper really lock in there solidly? I don't know because the upper fireback I took out was warped and didn't function properly. If so, any tips or explanation on how the hockey stick connects to the damper handle? The instructions in my rebuild kit explained that there's only one way for this to go, but weren't very clear on explaining exactly HOW that was.

Also, Tech Dude, does the primary air shutter open and close on it's own, or does it stay in the position you set it with the air control handle?

Thanks a ton,

Matt

 

[Free Monomoy]

hey matt,
are pushing back the damper hockey stick far enough? On the 0028, forward, or 5 O'clock is open, pushing it back to 730 closes the damper, and then further pushing back with some mild force to 9 O'clock locks the damper closed and creates a full seal for Cat Mode. It's a common problem that people have b/c they are unaware of the additional notch and/or afraid to apply the force needed to lock the damper.

i'm not tech dude, but my call on your second question is that primary stays in the position that you set it at. thankfully....one automatic transmission is enough for me.
Set the gearshift for the high gear of your soul.

cheers,
Darren

 

[homebrewz]

There is also a little raised relief depiction of a full circle and an open circle on the side of the stove to tell you
which position has the damper open and which one is closed.

I remember putting that back together was tricky. Maybe someone has a photo?

Be careful of letting the damper fall back too hard. It can smack the top of the fragile refractory package and crack it over time.
I've read where some have welded a support bar across the top of the package to stop this from happening. Seems like a good idea.
That little strip of metal on top is just a heat shield.. it doesn't do much to protect the top of the refractory.

Best of luck.

 

[Free Monomoy]

Does anybody have advice on changing out the secondary air probe/thermostat. Is it one part or will I be ordering more than one for the 0028?
Any help is appreciated. Thanks

 

[homebrewz]

The probe and coil are all one piece. From there, it attaches to the metal door for the secondary air intake by a metal spring or wire. I can't remember which.
Start by taking the cover off the back (two screws), and then unscrew the probe assembly and unhook it from the door. It will slide right out. The probe end
should be shiny metal.. maybe it just needs a clean up?

 

[Tech Dude]

There is the probe assembly by itself. The rest of the parts include the link, two screws, a shim and the door. You may not need all these parts.

 

[phishheadmi]

All right...got everything installed last night and have been burning since!! Darren, you were right about my not pushing the damper back far enough...I had to really reef on it to get it locked, but it's starting to loosen up a bit...I think the new gasket on the upper fireback was just really tight. I'm still working on getting my burn dialed in, but I suspect that will take a bit of practice. Thanks again for everyone's advice/expertise, it's been more than helpful!

Matt