Harman XXV has gremlins - help!

[beo10950]

Good morning and I need some guidance, please.

I own a Harman XXV, which I purchased new in September of 2011. It is cleaned weekly, the flue was cleaned annually and again yesterday, it uses 2 1/2 tons of quality pellets a season and has had the following parts replaced;

• Combustion motor (2024) OEM
• Control board (Dec 2025) OEM
• ESP (Dec 2025) Aftermarket- Red (I did also adjust the Dip switch to accommodate the switch from a black wired ESP to Red)
• Distribution Motor (Feb 2026) Aftermarket
• Flange gasket (Feb 2026)

Starting in November the unit started not shutting down and I was forced to open the hopper lid and leave it open until the fire extinguished. (This still occurs)
Then the distribution motor started slowing down and not really coming up to speed. It finally died last week and was replaced yesterday.
Today the unit fired up fine and was set to room temperature, 70 degrees and feed adjustment to 4. Once it came up to temperature the distribution motor slowed to a crawl, and did not reagin speed, even though the unit kept feeding pellets as the house temperature dropped to 65.

I do have a new door gasket which I haven't installed, but the only part which I have not replaced is the vacuum (differential) switch.

Could either of those items failing create my issue??

Any help/suggestion are greatly appreciated.

 

[NS P-68]

It sounds like a control board issue. However its also possible that an aftermarket distribution blower could also be an issue. Some of those blowers are not compatible with a speed control . A good starting point would be to take a voltage reading going to the distribution blower. In the meantime, you could try running the stove on constant mode and see if the distribution blower acts the same.