Harman PB 105 Pellet Boiler: Help solve some mysteries please

[JeffinVermont]

I recently bought a house with a Harman PB105 Pellet Boiler that provides heat and hot water along with an oil furnace. This forum was helpful in solving my first set of issues. Thanks! Now that I got the boiler cleaned and test fired for the coming winter, I have these mysterious issues:

1. I have a seldom-used zone in my house for a work space adjacent to my garage. When we bought the house, the valves for the plumbing leading to that zone were closed. When I open them, the don't get hot when using the oil furnace alone. When I got the pellet burner working, I got heat to this zone for the first time, which was great. Except that the zone never turned off when the temperature exceeded the thermostat. Even turning the thermostat to the minimum temperature had no effect.
2. At the same time, another zone (over the garage) also didn't turn off when the thermostat temperature was achieved.
3. Some accompanying information:
   • To solve my first set of issues, my plumber installed a new pressure relief valve, expansion tank and pressure/temperature gauge.
   • When I look at the temperature/pressure gauge, it read 208 degrees (F). Pressure was about 20 psi.
   • The outside temperature has been cold in the mornings (when I fired up the boiler) but balmy in the afternoons (60+ degrees).
   • I talked to my plumber, who isn't that familiar with pellet boilers, who had these theories:
     • The reason the two zones aren't turning off is that they are a "dump zone" for when the temperature gets too high. My gut sense is that 208 degrees is too high. I set the minimum temperature to 160 degrees and the maximum to 175. These are the settings when we bought the house. So, a readout of 208 seems like a problem.
     • With the outdoor temperature so high, this might be driving the high temperature. I don't understand how this can be but I also see a table in my manual (p.23) that addresses "Pellet Boiler Outdoor Air Reset Operation", with seems to have adjustments for the outdoor air if you have an Outdoor Sensor. I don't know whether I have one of these are not. Could this be the source of this issue?
     • The pellet feed rate is set at the middle of the range. I don't know what effect the pellet feed rate has on performance. Should I be changing this as the temperature outside goes up and down?
     • I've uploaded a couple of pictures of the setup.

If anyone has any thoughts on this, I'd be appreciative. Thanks.

 

[Tonty]

I’m not that familiar with pellet boilers, mine is a wood fired boiler. But it sounds to me like those could be dump zones, and they were activated because the set temp was exceeded. Did you have the upper limit set to 175 before the 208 readout? It seems to me that would be a problem. I would think that a pellet boiler shouldn’t exceed its upper set limit.
The 20psi sounds correct with 208 degrees. I’ve been told my pressure should be around 10% of the temp.

 

[PassionForFire&Water]

Dumb zones or thermal siphoning

 

[JeffinVermont]

I’m not that familiar with pellet boilers, mine is a wood fired boiler. But it sounds to me like those could be dump zones, and they were activated because the set temp was exceeded. Did you have the upper limit set to 175 before the 208 readout? It seems to me that would be a problem. I would think that a pellet boiler shouldn’t exceed its upper set limit.
The 20psi sounds correct with 208 degrees. I’ve been told my pressure should be around 10% of the temp.

Thanks for the reply. Yes, the upper limit was set to 175. Since your reply and Passion for Fire's, I did a little googling around on dump zones and it sure sounds like what's happening to me. Time to get a plumber/HVAC person in that's familiar with these systems!

 

[JeffinVermont]

Dumb zones or thermal siphoning

Thanks Passion...you're the second vote for dump zones....time to get an expert in.

 

[Mr._Graybeard]

The PB105 has an overheat light that will illuminate when the dump zone circuit is energized. It also will shut down the feed and require a reset before it runs again. Info is in the manual -- here's a link.

 

[JeffinVermont]

Interesting. I didn't notice the light come on during the "event". And the pellet feed definitely did not shut down. It got me to wondering about how the pellet feed works. Is it just a constant feed, or does it ebb and flow as the need for heat ebbs and flows? And what would be the thought process when setting the feed rate? I'm guessing trial and error, but what might I look for? If I set it too low, will I have the oil boiler kick in too often? And too high, wasting heat? The manual is silent on this topic.

I found this post from 2008 to be helpful in understanding how these boilers work. In particular the part about shoulder season operation. It sounds like I should only be running these when there's a need for them to be constantly on. Regardless, though, I'd feel more comfortable if the boiler shut off when the water got too hot.

Thanks for your help.

 

[Mr._Graybeard]

A wood boiler is a completely different animal in that the fuel supply is not regulated like a pellet unit. The Harman slows pellet feel intervals as it approaches maximum temperature. I don't think your boiler should come close to overheating with the max set to 175. I set mine at 180 with no problem.

The 105 can crank the heat but it doesn't deliver as quickly as a fossil fuel burner. During shoulder season you might have some cold startups, which can produce condensation and creosote. To reduce that you can fire the oil boiler to get the hydronic system up over 140 degrees. Or start the 105 without the circ pumps running, get it up to max temp and then run your zones for a couple minutes to introduce just enough cold water to drop the boiler temp to 140 or higher. Then shut the zones down and let the boiler catch up.

The 105 came with a couple different ignition systems: the traditional finned igniter that fits in the burn pot cavity and a much better "pressure igniter" in later models that directs superheated air directly on the pellets in the burn pot. After my boiler finishes introducing a startup quantity of pellets in the pot, the pressure igniter takes only 45-50 seconds to light them. The finned igniter can take several minutes.

For that reason the shoulder season can be a headache for people using a finned igniter. Open the trap door on the burn pot and you should be able to see the finned igniter if you have one.

 

[JeffinVermont]

Thanks. I'm pretty sure it's a finned igniter, as it takes a few minutes for sure. I'm away from home right now and can't check, but that's my guess. This is great information for me once I get the overheating/dump zone issue solved.

 

[White00s10]

If the only expansion tank is the one on your pellet boiler, Id upgrade to a larger one, or run two of the same size. There's A LOT of water in the water jacket of that pellet boiler, and the only way I could get mine to run pressure below 20psi was running 2 expansion tanks ( I did this when I moved my pellet boiler and plumbed it in correctly with the rest of the baseboards in parallel with my propane boiler. I ran into your exact situation almost 3 years ago, except my PB-105 was disconnected in my basement when I bought my house. It's been two seasons of me tinkering and tuning, but I finally got the boiler running great!

Here's my two threads.

Harman PB105 Questions. New Owner

Hello All, Been a lurker and reader for a few months , this is my first post. Buckle Up, Its gonna be a long one. X-D So back in May of 2020, I closed on my first house. The house had an oil boiler (Converted to propane, and a Harman PB105 Plumbed in series. House is 1400 Sq ft The boiler was...

www.hearth.com

Fixing my PB105

Hey everybody. When i bought my house in May of 2020, there was a Pb105 in the basement disconnected in the basement. It was apparently in good working order, but was vented wrong ( and poorly, from what I'm reading here), so rather than fix it, they just cut power and pulled the pipe. They...

www.hearth.com

 

[JeffinVermont]

If the only expansion tank is the one on your pellet boiler, Id upgrade to a larger one, or run two of the same size. There's A LOT of water in the water jacket of that pellet boiler, and the only way I could get mine to run pressure below 20psi was running 2 expansion tanks ( I did this when I moved my pellet boiler and plumbed it in correctly with the rest of the baseboards in parallel with my propane boiler. I ran into your exact situation almost 3 years ago, except my PB-105 was disconnected in my basement when I bought my house. It's been two seasons of me tinkering and tuning, but I finally got the boiler running great!

Here's my two threads.

Harman PB105 Questions. New Owner

Hello All, Been a lurker and reader for a few months , this is my first post. Buckle Up, Its gonna be a long one. X-D So back in May of 2020, I closed on my first house. The house had an oil boiler (Converted to propane, and a Harman PB105 Plumbed in series. House is 1400 Sq ft The boiler was...

www.hearth.com

Fixing my PB105

Hey everybody. When i bought my house in May of 2020, there was a Pb105 in the basement disconnected in the basement. It was apparently in good working order, but was vented wrong ( and poorly, from what I'm reading here), so rather than fix it, they just cut power and pulled the pipe. They...

www.hearth.com

This is super-helpful, thanks. I have the professionals coming on Monday. I'll print this out and hand it to them if they're puzzled at all. Heating systems are not my specialty. I thought I might be able to get by on my own, but it's time for folks that know what they're doing.

 

[White00s10]

When I purchased my house, the previous owner had a PB105 in the basement, The chimney was cobbled together out of single wall dryer vent, the unit was disconnected, but wired in such a way that if power was applied to the boiler, the circulator pump would run constantly. The inside of the fire box was absolutely filthy, with fly ash in the rear chamber of the burn box (where the exhaust fan goes) filling the pipe to the point where it was covering the ESP. I proceeded to apply power to the unit after a thorough cleaning, and lit it manually ( there was no ignitor lol) and when the unit got to 180degrees, water was dribbling out of the pressure relief valve because the unit was pushing upwards of 30PSI system pressure. The PB105 has 50 gallons of water in its jacket alone, coupled with the water in the system itself, and you could be seeing excess system pressures at full temp. I currently have 2 tanks, the 2.5 Gallon one that's on my oil boiler plumbed parallel with the PB-105, and a 4.4 gallon one I plumbed right after the pellet boiler.

A word of advice, consider stocking up on a few spare items on your pellet stove,

An ESP ( exhaust sensor probe)- geos into where the stove pipe attaches to the unit.
An Aquastat Probe - goes into the top of the water jacket
An ignitor.

These will make it easy to replace in the dead of winter on the off chance any one of these fail.

While I have a single zone, Here's how I have my unit set up. My boiler is set to run at whatever min / max I have set to on the unit. Whenever there's a call for heat from my thermostat, it send a signal down to a taco relay controller mounted on the wall. that in turn kicks on the circulator pump, which's circulates hot water thru the house. Call for heat is satisfied, thermostat stops sending signal, circulator pump kicks off, unit reaches its max temp by reading the signal from the aquatemp probe in the top of the water jacket, unit shuts down.

I took the time to study some of the pictures of your setup, and I noticed a strap on aqua stat on the top pipe coming out of your unit. I'm willing to bet that aqua stat is tied into a controller for a separate dump zone, and is either faulting on, or set in such a way that any excess temp over 200 is bled off into that circuit. The sole purpose of the outside air temp sensor is to lower your min/max of the unit as the outside temps begin to climb, thus saving energy.

Also, The PB105 has its own overheat safety shutoff. when the aqua temp probe measure temps over 210 degrees in the top of the water jacket, the unit goes into over temp shut down, and the blue power wire on the side of the unit is energized with 120VAC to either energize a normally open zone valve, or to power a circulator pump to active a dump zone and bleed off excess heat. See Page 21 of the owners manual

As for your feed rate, you ideally want it set so that there's 1 inch of ash between the burning pellets and the edge of the burn pot. Too high, and you'll waste fuel and push unburned pellets into your ash pan. To low, and till take forever for your unit to get back up to temp after a call for heat.

If no ones said it yet, take the time to download the manual from Harman's website and give it a read over.

https://downloads.hearthnhome.com/installmanuals/pb105.pdf

I hope this information helps. If there's any more, just ask. The unit looks complicated, but in all honesty, its a pretty simple but reliable machine.

 

[Mr._Graybeard]

Glad to hear the unit is working well for you, White00s10.

 

[JeffinVermont]

When I purchased my house, the previous owner had a PB105 in the basement, The chimney was cobbled together out of single wall dryer vent, the unit was disconnected, but wired in such a way that if power was applied to the boiler, the circulator pump would run constantly. The inside of the fire box was absolutely filthy, with fly ash in the rear chamber of the burn box (where the exhaust fan goes) filling the pipe to the point where it was covering the ESP. I proceeded to apply power to the unit after a thorough cleaning, and lit it manually ( there was no ignitor lol) and when the unit got to 180degrees, water was dribbling out of the pressure relief valve because the unit was pushing upwards of 30PSI system pressure. The PB105 has 50 gallons of water in its jacket alone, coupled with the water in the system itself, and you could be seeing excess system pressures at full temp. I currently have 2 tanks, the 2.5 Gallon one that's on my oil boiler plumbed parallel with the PB-105, and a 4.4 gallon one I plumbed right after the pellet boiler.

A word of advice, consider stocking up on a few spare items on your pellet stove,

An ESP ( exhaust sensor probe)- geos into where the stove pipe attaches to the unit.
An Aquastat Probe - goes into the top of the water jacket
An ignitor.

These will make it easy to replace in the dead of winter on the off chance any one of these fail.

While I have a single zone, Here's how I have my unit set up. My boiler is set to run at whatever min / max I have set to on the unit. Whenever there's a call for heat from my thermostat, it send a signal down to a taco relay controller mounted on the wall. that in turn kicks on the circulator pump, which's circulates hot water thru the house. Call for heat is satisfied, thermostat stops sending signal, circulator pump kicks off, unit reaches its max temp by reading the signal from the aquatemp probe in the top of the water jacket, unit shuts down.

I took the time to study some of the pictures of your setup, and I noticed a strap on aqua stat on the top pipe coming out of your unit. I'm willing to bet that aqua stat is tied into a controller for a separate dump zone, and is either faulting on, or set in such a way that any excess temp over 200 is bled off into that circuit. The sole purpose of the outside air temp sensor is to lower your min/max of the unit as the outside temps begin to climb, thus saving energy.

Also, The PB105 has its own overheat safety shutoff. when the aqua temp probe measure temps over 210 degrees in the top of the water jacket, the unit goes into over temp shut down, and the blue power wire on the side of the unit is energized with 120VAC to either energize a normally open zone valve, or to power a circulator pump to active a dump zone and bleed off excess heat. See Page 21 of the owners manual

As for your feed rate, you ideally want it set so that there's 1 inch of ash between the burning pellets and the edge of the burn pot. Too high, and you'll waste fuel and push unburned pellets into your ash pan. To low, and till take forever for your unit to get back up to temp after a call for heat.

If no ones said it yet, take the time to download the manual from Harman's website and give it a read over.

https://downloads.hearthnhome.com/installmanuals/pb105.pdf

I hope this information helps. If there's any more, just ask. The unit looks complicated, but in all honesty, its a pretty simple but reliable machine.

Thanks for taking the time for these detailed thoughts. Much appreciated! I admit that a lot of what you say is going over my head, but that's ok. I do have the manual, and thanks for pointing out p. 21. I hadn't noticed the status light message descriptions before. I also didn't notice any blinking when the dump zone was activated. But the temp only got to 208, not 210.

As for your advice on what to keep on hand, these questions:
1. I don't see any wires going into the stove pipe, at least from outside the unit. Maybe the ESP goes in from inside and I can't see it?
2. That aquastat sensor wire has me puzzled. It just dangles down the well, and the other end disappears into the boiler unit. How easy is that to swap out myself? My regular plumber, who isn't well versed on pellet boilers said that he's seen some people stuff insulation in there.
3. Graybeard mentions that the newer igniters are better than the older (which I assume is what I have). Can a new ignitor replace an old ignitor?

In any case, this gives me some fodder to discuss with the folks coming out to look at it on Monday. Thanks again!

 

[White00s10]

The esp is either a red or black wire running along side the unit that is screwed directly Into the stove pipe. The esp and the aqua temp sensor run under the front of the unit to the back of the board where they plug in. Your unit is likely not entering a dump zone condition because the aqua stat ( the gray box strapped to the pipe on top) is energizing another zone, causing the hot water to bleed off. As for the aqua temp probe sitting in the well on top of the unit, just make sure it's making proper contact with the well wall ( some people put copper wire in the well to act as a heat sink to make sure the aqua temp probe makes contact) but make sure the probe isn't directly touching the bottom of the well. I've attached some pictures of the aqua temp probe and the esp.

 

[JeffinVermont]

Your unit is likely not entering a dump zone condition because the aqua stat ( the gray box strapped to the pipe on top) is energizing another zone, causing the hot water to bleed off

Did you mean to say "is not" or "is? The "experts" came today but they sent the wrong people (not experts). They knew nothing about pellet boilers. Waiting for the one person they have that can help. We did crank the system up again today, and we had a repeat of the 208 degrees and dump zoning. And it was cold outside today (30 degrees).

 

[White00s10]

The pellet boards control board is likely NOT entering a dump zone condition, because the Gray box strapped to your output pipe on top ( which is a separate strap on aqua stat that did not come with the unit from the factory) is likely energizing and causing the garage circuit to open to bleed off the excess heat before the unit boils over. I'm gonna take a swing here and say something is likely wrong with your board or Aquatemp probe, causing the unit to constantly go into overtemp, So they put a strap on aqua stat on it to bleed the excess heat out into the garage. When whoever comes in to look at your boiler gets there, ask them too trace where the wires to that gray box go. Ill bet they got to a circulator pump or relay box that controls the garage circuit. I bet if you shut that relay off temporarily, the unit will go into over temp and shut down.

 

[JeffinVermont]

Thanks again for your help. I'll have your advice handy!

 

[JeffinVermont]

Mystery has been solved. Thanks to all on this forum that offered advice. I got a plumber that had some familiarity with these systems to come out about a month ago. He diagnosed the issue as the aquastat sensor. He ordered a new one, and made it back out here a couple of weeks ago to install it. We got the boiler fired up, and it's now maintaining a nice, steady, 170 degrees. Hurray! If the sensor goes out again, I should be able to handle that repair myself.

I have some lingering questions about the care and feeding of the boiler. I've been going through about three bags of pellets a day.

1. I'm puzzled about what the pellet feed adjustment does. When I moved in, it was set to "3", and I've kept it there. The last few days have been warm (40s and 50s), and it seems silly to burn through that much pellet. So, I turned it down to 2 yesterday and 1 today. The warming trend is continuing here in southern Vermont. What effects should I be looking for? I'm listening for the oil boiler to kick in to signal that I'm not generating enough heat from the pellet boiler. Is this a reasonable approach? What are the advantages/disadvantages of a slower or faster feed?

2. The manual says that I should be scraping down the burnpot holes every few days, and that I can do that while the boiler is in operation through the firebox door opening. Really? I'm not excited about sticking my hand into that opening while a fire is raging. Presumably I should turn the minimum temperature dial to "off", wait for the fire to die down, and then go in. And if I'm doing that, it seems like I'd do a much better job by swinging the hopper door open. I can't really see what I'm doing coming in through the firebox door.

Thanks for everyone's help, and happy New Year to all!
Jeff

 

[Mr._Graybeard]

The thing you don't want to happen is for the boiler temp to fall much below 140 degrees. A cold boiler produces creosote, which can be corrosive as well as messy. With the finned igniter, you're going to have trouble maintaining that if you don't keep the minimum temp pretty high, like 170 at least. If I were you I'd watch that boiler temperature closely during warmer weather because it's easy for cold water from the heating loops to knock the temp down quickly. A number of people have even added buffer tanks to store heated water and keep that boiler temp in range.

I think the consensus on the forum is to set the feed rate and 4 and forget it.

 

[White00s10]

I'm with Mr Graybeard. I have mine set at 4-4.5 feed rate. Ideally you want the ash to be around an inch from the edge of the burn pot. A lower feed rate won't really save pellets, while it will use less, it'll take longer to reach to temp.

As for scraping the burn pot. I usually just give the clean out rods on the side of the boiler a pull once a day. Than once a week, I turn the min and max to off, let the fire go out, swing open the hopper door and clean the burn pot. This involves vacuuming out the ask in the burn pot, scraping out the carbon, and vacuuming out the area where the ignitor is.

I usually try to keep my mind temp set around 165/170. That way by the time the unit fires ( I too have the finned ignitor) it's around 150-155. Like Graybeard said, prolonged burn with water jacket temps around 140 causes creosote and that's no bueno.

 

[Mr._Graybeard]

Yep, scraping is easy with the swing-out hopper; I can't imagine doing it through the firebox door. Pellet quality can affect how quickly carbon builds up. I burn a lot of cheapies, so I scrape after going through a couple hoppers, like, eight bags. But during the recent cold snap I let it slide for about three times that long. The boiler was just running constantly for days.

 

[JeffinVermont]

Yep, scraping is easy with the swing-out hopper; I can't imagine doing it through the firebox door. Pellet quality can affect how quickly carbon builds up. I burn a lot of cheapies, so I scrape after going through a couple hoppers, like, eight bags. But during the recent cold snap I let it slide for about three times that long. The boiler was just running constantly for days.

Thanks for the responses Graybeard and White00s. I've set my feed rate back to 4. I noticed that the temp dropped to about 150 when I slowed the rate down. And I'll continue to scrape the grate every few days after a brief shutdown. And pull the rods every time I visit the boiler, at least once a day.

We were given the impression by the prior owners that we'd go through one bag a day. It's more like three. I'm keeping a daily log to see how much it might change based on outdoor temperature (it's been super mild the last few days, and also into this week).

Thanks again!
Jeff

 

[Mr._Graybeard]

In January with highs in the teens, lows around zero, I go through four bags a day. I heat a century-old farmhouse, so a somewhat leaky house in an exposed location.