My PB105 Pellet Boiler

Two years ago, I decided to replace my oil boiler with a Harman PB-105 Pellet Boiler.  So far, I’ve been extremely happy with it; however, it has not been without pitfalls.   I live in rural Alaska, so failure of my boiler when the temperature outside is -50F can be disastrous.  Our temperatures also require that we burn lots of pellets – so my boiler has been used heavily.  As a result, I’ve learned a few critical things that Harman really needs to flesh out in their product manual.  The following are some tips and considerations if you decide to install this system. 

Disclaimer:  These are a list of things I do to maintain my boiler.  I am not a boiler mechanic and you should check with a professional.

To begin with, the product manual describes many things that have to be cleaned on boiler.  Read this carefully – every page, every paragraph, and every word!  There are a lot of one sentence statements in the manual that are critical and easily missed. 

Cleaning is critical to safe and efficient operation of this boiler.  I am guessing that many problems people experience with this system – from burnt out igniters to failed augur motors - stem from inadequate or improper cleaning. 

1) The burn-pot is the first place that has to be cleaned.  The manual does a fairly good job explaining what to do here (page 31) – but you need to read this page carefully.  As they suggest, scrape any carbon down into the bottom of the pan.  This is correct, but only the first step.  What they may not explain is that the system works by passing air over an igniter element below the burner pan.  This hot air flows first through the holes in the burn pan and then through the pellets themselves, igniting them.  If the air holes in the burn pan get plugged with carbon, the airflow is retarded and the igniter can overheat without lighting the pellets – and possibly burn out your igniter.  If you see these holes getting clogged, take a small piece of wire or toothpick and poke it into them to ensure they are open and can allow air to pass. 

2) As the manual describes, remove the metal cleanout cover.  This is a plate below the burn pan that allows access to the igniter.  Two thumb (wing) screws hold it in place.  Once the plate is removed, vacuum out any ash that has accumulated around the igniter.  This will ensure adequate airflow and faster start times, minimizing burnout of the igniters – which are costly to replace.

3) Speaking of the igniter, you should know that these igniters are prone to failure. Consider keeping a spare as a backup so that you can replace it on the weekend if the dealer is closed.   Fortunately, replacing these igniters is fairly straightforward.   First, cut the power to your system.  Remove the small plate under the burnpot (see step 2 above).  Next, remove the metal bracket holding the igniter in place. You’ll see where the wires run to the right, back through a caulk plug that helps keep air from flowing in, and then to the power supply.  Disconnect these wires from the power supply.  Cut the caulk plug and remove the wires with the old igniter.  Replace the igniter in the opposite fashion. This can be tricky as the wires are fairly short.  You’ll need to replace the plug where the wires lead through the box to their igniter. I used a heat-safe silicon sealant to reseal the wires and prevent airflow from entering at this point. 

4) When the system is run on automatic ignition, it may constantly turn off and then re-ignite - particularly in warmer weather.   This can cause premature burnout of the igniter.  Consider running the system in manual mode to minimize this.   During warmer weather, I turn the feed rate down to 1 so that it takes longer to heat the tank, keeping your fire lit.  Don’t forget to turn the feed rate back up when the weather gets cold.  After time, you’ll get a feel for what the feed rate should be for your house and a given outdoor temperature. 

5) If you run the system in manual mode, be sure that your plumber (or you) has installed a heat dump loop.  This loop should have a normally open zone valve.  When power is fed to the boiler and it is operating normally, the valve remains closed.  Should the boiler lose power, it opens and allows heat to “dump” into the loop, preventing an overheat situation. 

6) Consider a battery backup, available from Harman, to keep the system running should you lose power.   Should your system be burning when the power goes out, this will allow it to keep burning. Without this, you risk smoke backing up into your house when the exhaust fan loses power and is unable to pull the smoke through the chimney.

6) The manual also describes removing the feeder cover (p31, figure 20).  This is essential.  As pellets feed into the augur, fine dust is caught below a plate in a small compartment where the augur goes into the firebox.  This dust can accumulate and choke operation of the augur.  To remove the dust, look for the access plate shown in Figure 20 under the hopper.  There is a small cover held in place by a single thumb screw.  Remove it and vacuum out any fines that accumulate.  If you don’t do this, you will tax the motor and eventually burn it out.

7) If you do burn the augur motor out, it is easy to replace. There are three screws that hold the motor to the feeder gear motor bracket.  There is also a set-screw that holds the motor onto the spindle. Disconnect the power from the boiler.  Next, disconnect power to the augur motor by disconnecting the two wires that run from it.  Remove the set screw.  Remove the three screws that hold the motor to the bracket.  Now, replace it with the new motor.  Be sure the set screw is tightened against the flat side of the spindle.  Be sure to keep the old fan blade that is mounted on the motor; mount it on the new one.  This is designed to keep the motor from overheating and burning out prematurely.

8) Evidently, Harman had issues with the first generation of these augur motors.   Mine was replaced under warranty.  There is a small gear within the motor that becomes warn, causing slippage.  Mine was worn on one side by only about 1 millimeter on the side where it motor engages the slide plate assembly, but this was enough to cause a failure. If you have a bad motor, once you’ve removed it, you can open the case up to see if you have an older model or the newer.  Those with have dark gray/black gears are the older model.   The new ones have a white gear made of a more durable metal.   

8) Every inch of your chimney must be regularly cleaned so that the boiler has proper draft.   When you do this, be sure to remove and clean the combustion blower.  The fan blades on this blower become coated with soot, causing the boiler to move less air.  Use a brush to carefully remove the soot from these fan blades and from the entire assembly.  Low airflow will cause your flame to be smaller and you will burn pellets less efficiently. Eventually, you will get error messages and the system will shut down.   I bought an ash vacuum for this task as a regular shopvac will send soot everywhere.

9 ) Take time to clean the secondary ash chamber.  This will also help airflow.

10) At least once a year, use a brush to clean the interior of the boiler.  Soot buildup, particularly on the heater exchangers, will reduce the system efficiency.

11) Installation of the aquastat sensor can be tricky.  It fits into the brass well screwed into the top of the boiler and is wired back to the control panel.  If the aquastat fails to make firm contact with the sidewall of the brass well, the temperature reading will be off, causing the boiler to overheat.  Harman supplies a small spring to hold the aquastat against the well wall – but I found this doesn’t work well.   I put a piece of copper wire into mine to serve as a small shim.  Other plumbers recommend using a heat transfer paste here.  The problem with using these pastes, unfortunately, is that some pastes will harden, preventing you from removing and replacing the aquastat sensor later.  I didn’t want to risk this. The aquastat that Harman provides is flimsy – be careful handling it.  You might consider purchasing an extra one of these as well should yours fail.

 12) If your controlboard inexplicably loses power, check the fuse.  There is a 6 amp glass fuse on the back of the control board that is easily replaced.  These fuses are available at auto parts stores.  I keep some of these on hand as well.

I've found that the type of pellets I use also dramatically effects operation and efficiency of the system.  Different brands produce different amounts of ash and burn at different efficiencies.  Currently, my Harman dealer is stocking a brand out of Canada that costs about $30 more per ton - but is resulting in about half the ash.  I'm also burning less.   Track your pellet usage carefully to determine what works best for you.

With care, I expect I'll get many more good years from my pellet boiler.  Since I installed it, I've already saved about half on the cost of heating my home as compared to fuel oil.  In addition, because of the larger water reservoir, I've actually saved on electricity.  My old oil system was inadequately sized; my hydronic pumping was constantly pumping water through the zones.  Now, I always have a good supply of hot water at standby and my rooms are quickly heated, allowing the zone valves to close and turn off the pump sooner. 

If anyone has any other tips on operating the PB105, please feel free to list them below.