P68 Loss of draft at Differential Switch?

[jettech]

Bought and installed new in Oct. 2012. Has burned over a ton of pellets every year for 7 years with almost zero problems. Recently the auger made a horrendous metal on metal scraping noise so I shut the stove off. I unplugged it and manually rotated the auger backwards to see how it felt. It backed off fairly easily so I plugged it back in and started it. It made the same noise a couple more times but then it quieted down and started feeding normally. Now the auger and auger motor sound normal and feeds pellets same as before.

Now the problem is the stove won't complete the light off cycle. The auger quits feeding and the ignition shuts off.
I've been troubleshooting it but haven't determined the cause yet. It appears to me that the draft reference is very low at the differential switch. The combustion motor sounds good and the stove has a good draft.. It will pull the door closed from 1/2 inch open. With the combustion motor running I don't feel any draft on the 1/8 tubing that attaches to the differential switch. I installed a new switch and I have new rope seal for the doors but haven't installed it yet. I checked the combustion air ducting and inlet door. I clean the flu every year but I checked it and it is open. The other end of the 1/8 inch tubing attaches to the Ultra Feeder Weldment. Is there a chance there is a problem inside the weldment?

I disconnected the differential switch and jumpered the wires together so the stove would run. I also attached a volt meter across the switch so I could watch for continuity. The stove started normal and the draft appeared normal judging by the flame shooting straight up. The differential switch showed continuity for the first minute of the start but then went open.

Any assistance is appreciated.

 

[Don2222]

Hello
I would yank out the auger and clean and wire wheel the auger and auger chute and also blow out the vacuum hose. Just my 10 cents.
See my pics of some dirty Harman Augers here
https://www.hearth.com/talk/threads...n-over-10-years-see-pics.168620/#post-2263431

Also check for the Pox! Auger Pox!
See pic below of a 10 year old auger I just yanked out the other day that was in a Bosca Soul 700 FS made in
Huechuraba in the northern part of Santiago de Chili !! Can you believe it???
Easy fix, we just ground down all the ruff spots with a grinding stone.

 

[Ssyko]

thats some ugly yard bird excrement welding right there Don

 

[Mt Bob]

Possible vacuum hose problem.Possible problem(restriction) where the hose plugs into the firebox.Most likely,you're flue/exhaust is partially restricted/plugged.

 

[jettech]

Thanks for your helpful suggestions. I have found the problem and the stove is running perfect again. Turns out is was a self induced fault. After the auger made the awful metal on metal noise I had removed the fines door and vacuumed out the fines. When I put the door back on, I accidentally didn't get the slot in the top of it dropped down on the tab correctly so the tab was holding the fines door open creating a vacuum leak. The vacuum leak was very near the port for the hose that goes to the draft switch. I am once again humbled (still human) but glad it's fixed without spending much money.

We are very pleased with the Harrman P68 pellet stove. It has provided us with 7 years and counting of trouble free service. It lights off and comes up to temperature quickly. We love to sit by the stove in the winter and enjoy it.

 

[Mt Bob]

Thanks for your helpful suggestions. I have found the problem and the stove is running perfect again. Turns out is was a self induced fault. After the auger made the awful metal on metal noise I had removed the fines door and vacuumed out the fines. When I put the door back on, I accidentally didn't get the slot in the top of it dropped down on the tab correctly so the tab was holding the fines door open creating a vacuum leak. The vacuum leak was very near the port for the hose that goes to the draft switch. I am once again humbled (still human) but glad it's fixed without spending much money.

We are very pleased with the Harrman P68 pellet stove. It has provided us with 7 years and counting of trouble free service. It lights off and comes up to temperature quickly. We love to sit by the stove in the winter and enjoy it.

Do not feel bad,lots of Harman owners have made this mistake on the fines "door" "cleanout" Just happens.

 

[Harmanizer]

Yup.I done that.

 

[Ssyko]

yep me too!................... oh wait i don't have a Harman