Problems with a Tarm Pellet boiler

The only time I had a burn back was when some pellets got up behind the plate that holds the hopper door open while I filled it, which broke the seal on the hopper. I had also knocked in a bunch of fines that were on the sides of the auger channel. That was the only issue I had. I use the factory recommended settings for auger and air and operate in auto 100-30%. Also have a barometric damper installed with a manometer to monitor draft. Only thing I could recommend is checking all the gaskets on the hopper. If there is a bad seal, that would allow a burn back.

We have a 2.5 MH that we installed last summer. We have had one unexplained burn back about 2 weeks ago that I believe was related to the amount of fines that built up in the channel which holds the auger. The lower third of the auger channel was packed with saw dust and I believe as the hopper got down to the last 25% the fire burned back in the saw dust. I called Tarm the next day and the tech support said the unit could burn back with just the air left in the mostly empty hopper. We have the oversized hopper on our unit which has a flat floor and a large portion of the pellets will stay on the sides of the hopper and not slide into the auger channel. Our hopper seal was tight so now my insurance policy is to make sure the hopper stays at least 50% full at all times. cleaning and resetting back to operational took a good 4 hours so I don't want to do that very often.

We have burned 3 types of pellets this year (7.1 tons burned so far) and next year I will be much more selective with my pellet purchases. The Tarm dealer said the pellets would not matter much but I have good data showing big differences in ash, clinker formation, saw dust and lbs per HDD. I think fines and clinkers are the biggest concerns for this unit.

I think the unit is much more worry free if it idles as little as possible. I set our unit to run at 51K as MID High and a ~65K BTU/Hr 3/4 high setting to try and keep it running longer to minimize idle time. Tested efficiency has been 84-85% with Testo flue gas analyzer which I am very pleased with. It's not perfect but for our house this has allowed us to stop burning oil and the house is warmer than last year when we were constantly turning down the thermostats to cut consumption.

My friend has one and he switched from corn to pellets and had the samething happen and he slowed down his blower speed and the problem went away.

The most likely cause of a burnback with that design, in my experience, is an oversized boiler.

Do an accurate heat loss analysis on the house (or have one done), and compare that to the boiler size.

Joe

BrownianHeatingTech said:

The most likely cause of a burnback with that design, in my experience, is an oversized boiler.

Do an accurate heat loss analysis on the house (or have one done), and compare that to the boiler size.

Joe

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Why would an oversized boiler cause a burn back? The output is fully adjustable and a boiler is sized for a worse case scenario so 100% is not necessary with any appliance all the time. My heat loss calc just exceeded the output of a 2.5 so I should have gotten an undersized appliance? The only burnback I've had was when some pellets were breaking the seal of the hopper. If the appliance is idling maybe someone has the auger time for idle set too long resulting in a burn back. I'd check the gasket on the hopper door, side access panels and auger motor for leaks.

whippingwater said:

BrownianHeatingTech said:

The most likely cause of a burnback with that design, in my experience, is an oversized boiler.

Do an accurate heat loss analysis on the house (or have one done), and compare that to the boiler size.

Click to expand...

Why would an oversized boiler cause a burn back? The output is fully adjustable and a boiler is sized for a worse case scenario so 100% is not necessary with any appliance all the time. My heat loss calc just exceeded the output of a 2.5 so I should have gotten an undersized appliance? The only burnback I've had was when some pellets were breaking the seal of the hopper. If the appliance is idling maybe someone has the auger time for idle set too long resulting in a burn back. I'd check the gasket on the hopper door, side access panels and auger motor for leaks.

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If the unit is oversized, it will idle a lot (since there is nowhere for the heat to go), allowing opportunity for a burn-back.

Joe

BrownianHeatingTech said:

whippingwater said:

BrownianHeatingTech said:

The most likely cause of a burnback with that design, in my experience, is an oversized boiler.

Do an accurate heat loss analysis on the house (or have one done), and compare that to the boiler size.

Click to expand...

Why would an oversized boiler cause a burn back? The output is fully adjustable and a boiler is sized for a worse case scenario so 100% is not necessary with any appliance all the time. My heat loss calc just exceeded the output of a 2.5 so I should have gotten an undersized appliance? The only burnback I've had was when some pellets were breaking the seal of the hopper. If the appliance is idling maybe someone has the auger time for idle set too long resulting in a burn back. I'd check the gasket on the hopper door, side access panels and auger motor for leaks.

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If the unit is oversized, it will idle a lot (since there is nowhere for the heat to go), allowing opportunity for a burn-back.

Joe

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Yes idling provides the opportunity for burnback, but it is not a cause. If that were the case even a properly sized boiler would be problematic on warmer days.

whippingwater said:

Yes idling provides the opportunity for burnback, but it is not a cause. If that were the case even a properly sized boiler would be problematic on warmer days.

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The more oversized the boiler is, the more it idles.

Joe

Good Morning WW

Isn't it nice to have a salesman's ability for double speak? Your always right - even when you ignore the question parameters!

I am SO Jealous that I cannot twist facts like Jo can! Or should I be?

JO == Pal -- Buddy --- Let me try to help

WhippingWater asked: Why a 4.0 would be over sized to burn back, when its advanced feed controls can modulate its fuel input to load demand?

Certainly when fuel is reduced, the heat exchanger then becomes over sized - but how is the feed system over sized then when a fine appliance like this matches combustion air to available fuel rates?

Or are you simply blowing smoke again to raise your post count?

Morning Sting

I give up. I'm not a "heating professional" just a dumb truck driver and part time net builder. I will retreat to the comfort of my shop and hopefully someone will help the person who started the thread with an actual CAUSE for the burn back so they can correct it.

Sting said:

WhippingWater asked: Why a 4.0 would be over sized to burn back, when its advanced feed controls can modulate its fuel input to load demand?

Certainly when fuel is reduced, the heat exchanger then becomes over sized - but how is the feed system over sized then when a fine appliance like this matches combustion air to available fuel rates?

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Because it can't modulate down to 0%, Sting. The minimum output of a 4.0 is a hair under 41kbtuh.

So, when it is running at its minimum, but it is oversized, there may be a large percentage of the heating season when its minimum firing rate exceeds the heat load of the structure.

For example, if the heat load of the structure is 90kbtuh, that only occurs on the absolute coldest day of the year. And probably never occurs, since most heat load calculations include a substantial "safety factor." Even if 90kbtuh were accurate, a typical structure will see an average load that is half the peak load (approximately). So the average load for that structure would be 45kbtuh, which is barely above the minimum firing rate of the 4.0 boiler. At least a third of the heating season, and probably more than half of it, will see the boiler running at minimum, and still being oversized.

Now, when the boiler is running at minimum, there are two factors that come into play. First is the fuel flow rate, which is a bit above the level needed to prevent a burn-back. The other is the water temperature. When the water hits the high limit, the feed auger must shut down, in order to prevent the water from going over-temp. With no flow of fuel through the auger, the fire can start to burn back up the pile in the burner and work its way back into the auger, triggering the fire-suppression system and making a mess.

Joe

Again Joe you have not provided a cause. You described the operation and if the idle auger times and the hopper is sealed there should be no burn back with the exception as stated by a previous poster of an excess amount of fines.

whippingwater said:

Again Joe you have not provided a cause. You described the operation and if the idle auger times and the hopper is sealed there should be no burn back with the exception as stated by a previous poster of an excess amount of fines.

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There's nothing stopping the fire from burning back into the auger, other than the feed rate being above the burn-back rate. There is sufficient oxygen present for that to happen, even if the hopper is sealed perfectly. The sealing reduces the burn-back rate, so that it doesn't exceed the feed rate... unless the feed rate is limited by the boiler running at idle too much.

Joe

BrownianHeatingTech said:

whippingwater said:

Again Joe you have not provided a cause. You described the operation and if the idle auger times and the hopper is sealed there should be no burn back with the exception as stated by a previous poster of an excess amount of fines.

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There's nothing stopping the fire from burning back into the auger, other than the feed rate being above the burn-back rate. There is sufficient oxygen present for that to happen, even if the hopper is sealed perfectly. The sealing reduces the burn-back rate, so that it doesn't exceed the feed rate... unless the feed rate is limited by the boiler running at idle too much.

Joe

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So as long as the auger IDLE setting is correct and the hopper is sealed there will be no burn back. It has nothing to do with boiler size as you stated and confirmed in your last post. The feed rate cannot be limited too much by idling because the feed rate is adjustable for idle to maintain a fire. If there is are burnbacks because of idle simply increase the auger intervals for idle.

whippingwater said:

So as long as the auger IDLE setting is correct and the hopper is sealed there will be no burn back. It has nothing to do with boiler size as you stated and confirmed in your last post. The feed rate cannot be limited too much by idling because the feed rate is adjustable for idle to maintain a fire. If there is are burnbacks because of idle simply increase the auger intervals for idle.

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I apologize if I'm not explaining this well, but that's simply not correct.

Anyone who likes to can feel free to call BioHeat and confirm what I'm saying here.

This issue (proper sizing to avoid burn-backs) was the very first thing that they addressed when I initially met with them to discuss adding the pellet boilers to my offerings. Sizing is critical with these units, and oversized units will run the risk of burn-backs.

Joe

And the salesman dances rather than answer the direct question


AGAIN!

Sting said:

And the salesman dances rather than answer the direct question

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The question was answered.

I am curious why, in your mind, a "salesman" would tell someone to buy a smaller, less expensive product, though...

I mean, if I were selling a system with a MH boiler, I could make substantially more by selling someone an oversized 4.0, instead of a properly-sized 2.5 - why, pray tell, would I be telling folks to buy the less expensive boiler?

Joe

Sting,

I think Joe answered this correctly. The point is that if the boiler idles for an extended period with no demand for heat then the rate of burn back towards the hopper can be greater than the rate the new fuel is being pushed forward into the burning chamber. Eventually if the boiler stays in idle mode the fire will work its way back to the fire suppression sensor setting off the flood to stop the burn back. In my case I thought is was caused by the fines but it also would happen with just pellets. Tarm told me that there is enough O2 in the hopper to allow the fire to burn with no air leak.

Back on Topic:

One other things should be checked on the unit for which this thread was started. How is the dump zone configured for excess heat? In my case the dealer gave us a Tekmar 152 for controler of the dump zone and this is programable to call for heat once unit reaches idle temp with or without a delay. It might be useful to know if this unit has this installed or how the overheat is being controlled. I like what we have but I think it would be better if it had 1 or 2 more set points so we could have a longer open time with a larger delay (8+ minutes) with a 25+ differential to go with the short 10 degree differential with no delay. The longer open cycle delay would suck out more BTU's and cause the Tarm to ramp up to at least the 30% level for a few minutes to advance more fuel to prevent the burn back. The way ours is right now the boiler releases short bursts of heat into the overheat loop but not enough to force it into the 30% mode. I think you need both to accomplish the over heat protection and a regular demand for enough heat to start the 30% mode with some frequency like every 20-30 minutes.

The learning curve running for this boiler has been steep but it will be worth it once it is set up. I think back to the first thought of filling it and forgetting about it as it will auto run. That would be great but I think even the folks with the new MES PB's are finding that some user interface is required. I believe the daily maintenance is less than a stick wood boiler and that is what I was really after.

I have a different view -- but then I usually do

Whippingwater asked

whippingwater said:

Why would an oversized boiler cause a burn back? The output is fully adjustable and a boiler is sized for a worse case scenario so 100% is not necessary with any appliance all the time.

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And Jo responded that a smaller boiler is necessary

?????????????


Ahemmmmmm -- Excuse me but how was the direct question answered by our expert? - he simply injected -- once again - his opinion - not the reason that a correctly controlled 4.0 should burn back!
Or did I miss the fact that a 4.0 cannot be correctly controlled?
Its a poor design?
or - Should Any load that is correctly sized and operated, in the dead of winter operating with a 4.0 -- should that install or any 4.0 be immediately shut down and the load returned to a traditional fueled boiler once the weather moderates above a 30 point degree day? - Because its too large a boiler and now incorrectly sized for warmer days of operation ??????

Double speak is not an answer! Its what you do to get elected or get the sale and install. Buyer Beware! Boilers always run better when correctly sized -- I do not question that -- I would like to know why a fine product like the 4.0 might not be controlled - or trusted, to operate correctly in the shoulder months of use?

Or anytime -- as you point out this thread was started a few days ago

It was still cold

Heck its single digests tonight again

The auger interval for idle is fully adjustable from 1-60 minutes with 30 minutes the recommended setting. So, if the pellets are burning back at idle why can't the interval be reduced to say 25 minutes and push the pellets into the burn chamber sooner? This has been my contention all along, that the burnback can be controlled. This could result in some overheating at idle but I doubt it would be significant. Also the boiler will not operate unless the door is tightly closed engaging the micro switch safety switch.This feature is also to prevent burn back. The only burnback I've had was when I pushed a BUNCH of fines into the auger chamber and some pellets were under the hopper door gasket breaking the seal. Just because the appliance is at idle doesn't mean it WILL burnback. If that were the case , as Sting states, all these boilers would have a problem in the warmer times.

This boiler is the safest, most trouble free, easily controlled and convenient way I've burnt wood in my life, which is what we've always done. Joe has given the impression that these boilers have a design flaw that will result in a burn back simply because the appliance is at idle. THIS IS SIMPLY NOT TRUE. I'll agree with him that an oversized appliance will idle more and provide the OPPORTUNITY for a burn back, but, it is not the CAUSE. His opening statement was "in his experience" then when questioned he said it was how he understood what Tarm said. This is my experience with my boiler. They are one of the finest solid fuel burning appliances available in the USA. And I'm not a salesman.

Sting said:

I have a different view -- but then I usually do

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Apparently, someone else was able to understand what I was posting, so you may want to consider the possibility that you just don't have the knowledge or desire to understand the answer.

Sting said:

Or did I miss the fact that a 4.0 cannot be correctly controlled?
Its a poor design?

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It can be correctly controlled. Down to 30% modulation. It does not modulate down to 0%, like a mod-con gas boiler, or the like.

The design is not "perfect" (no boiler is), but it's pretty darn good, as long as it is sized and installed correctly.

Sting said:

Its what you do to get elected or get the sale and install.

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You still haven't told me why someone who's just looking to make sales, would tell folks to buy the smaller, less expensive boiler. Hmmm...?

whippingwater said:

This boiler is the safest, most trouble free, easily controlled and convenient way I've burnt wood in my life, which is what we've always done. Joe has given the impression that these boilers have a design flaw that will result in a burn back simply because the appliance is at idle. THIS IS SIMPLY NOT TRUE. I'll agree with him that an oversized appliance will idle more and provide the OPPORTUNITY for a burn back, but, it is not the CAUSE. His opening statement was "in his experience" then when questioned he said it was how he understood what Tarm said. This is my experience with my boiler. They are one of the finest solid fuel burning appliances available in the USA. And I'm not a salesman.

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There is no design flaw. It's a fine boiler, and I know many folks who have been running them happily for years. If the boiler is sized, maintained, and installed correctly, there should never be a burn-back, other than in the case of an extended power failure. In my experience, and as confirmed by the folks who build the things, the most likely cause of a burn-back (and, particularly, multiple burn-backs) is an oversized boiler. As I've said, anyone should feel free to call BioHeat and ask in that regard.

The "flaw" that results in that type of burn-back is an improper choice of boiler for a given heat load. Which is no fault of the boiler.

Joe

I'm not a salesman for these boilers either but I would like to know what is going on with the boiler in question with this thread. The folks at BioHeat were pretty attentive to my needs when I was doing the setup so I look froward to hearing what the solution is for this situation. I will make changes to our setup come spring when I shut it down for the spring / summer so next fall it is in place for a second successful season. I want any prospective Tarm MH owner to know I agree this is a great way to free yourselves from the fossil fuel world and in our case support local industry with an abundant renewable natural resource for the fuel we consume.

Westchoper said:

I'm not a salesman for these boilers either but I would like to know what is going on with the boiler in question with this thread.

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Indeed. Hopefully Sting hasn't scared the poster away, and we can get some real answers for someone who has a real problem, and needs help.

Joe

Sting seems to have his own agenda. Maybe he is selling a "fix". People have been kind to offer their expertise and should be treated in a polite way or their expertise will not be shared in the future.

You don't have to agree but ...