PF100 thermister problem - maybe

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thechknhwk

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Oct 22, 2010
10
St. Charles, MI
d14scrambler.com
Being the average schmo that I am I've been running into a series of problems with my PF100... I have already replaced the vacuum switch for the auger, but now I'm experiencing a reoccurring problem with thermister. Now that I have the pellets feeding again and got a good fire going and heat circulating to the house normally for the first time in 3 days. I was going to replace the combustion fan with a dual sided fan, but after turning the stove down to 60 deg to get it to ramp down so I can shut it off it just keeps feeding pellets, keeps burning, keeps kicking the squirrel cage blower on and circulating more heat. It's now well over 60 deg in here, but it won't stop cycling. I'm no HVAC guy, so I'm not sure where to go with this. Any suggestions greatly appreciated....

Thanks!!
 
I have the same furnace and have noticed ( read it on this forum to) the themistat is off by about 5 degrees, so at 60 it wants to heat to around 65. This might be why its not shutting down at that setting. Then they also like to run at idle mode ( helps prevent tempreture swings). Mine will hit its temp and then run on that ilde setting for a long time, and the blower ( distrabution) will kick on and off because the plenuim temp gets hot enough to activate the plenuin setting. That control has 3 settings, kick on, kick off, and over temp shut down. You set the temps you want that control to activate. Hope that helps you.
 
Thanks for the response. I too have noticed the thermister is off by about 5 deg. I have now turned the dial to "off" and it continues to feed pellets and supply heat to the house. Thermister still @60 deg and digital thermo for the AC says it's 72 deg.
 
Well if your themostat is off and it is still calling for heat makes me think of a few posibilitys. Is your furnace on Auto Mode ? Is your dial set on Normal Setting ? If yes to both these questions I would say for some reason your control board is not prossesing your themostates readings or there is a problem with the themostat its self.
 
bwep said:
Well if your themostat is off and it is still calling for heat makes me think of a few posibilitys. Is your furnace on Auto Mode ? Is your dial set on Normal Setting ? If yes to both these questions I would say for some reason your control board is not prossesing your themostates readings or there is a problem with the themostat its self.
Click to expand...

Under normal conditions I am on the normal setting for the burn temp, I have the feed rate set @4, and the igniter set to automatic and the the other dial set to automatic as well.

Another oddity - I turned the power toggle switch off to change the combustion blower fan blades and then when I turned it on the thermister still set @ 60, the stove doesn't feed or attempt to light. The current temp in the house is 70, I turned it up to 65, nothing yet. But it seems once the cycle starts it just won't quit burning no matter how low I adjust the thermister.

thanks for the response bwep.
 
Maybe you could try unhooking your thermostat leads, the "T" terminals at the furnace and read back up to your thermostat with a ohm meter. Have someone turn the knob back and forth to see if the resistance changes. You might have a bad connection.
 
thechknhwk said:
Being the average schmo that I am I've been running into a series of problems with my PF100... I have already replaced the vacuum switch for the auger, but now I'm experiencing a reoccurring problem with thermister. Now that I have the pellets feeding again and got a good fire going and heat circulating to the house normally for the first time in 3 days. I was going to replace the combustion fan with a dual sided fan, but after turning the stove down to 60 deg to get it to ramp down so I can shut it off it just keeps feeding pellets, keeps burning, keeps kicking the squirrel cage blower on and circulating more heat. It's now well over 60 deg in here, but it won't stop cycling. I'm no HVAC guy, so I'm not sure where to go with this. Any suggestions greatly appreciated....

Thanks!!
Click to expand...

First of all, what's a thermister????????????? Is that a Harman thing???????? OR, is it a thermostat like everybody is offering advice about???
 
The thermister is what they call the thermostat in the manual. It functions like/as the thermostat but it's not really one. I don't know what makes it different.
 
if you do find that its the thermister being off by a few degrees then just loosen the set screw on the dial, re-align the knob with a more accurate temp and re-tighten the set screw.
 
I remember discussions on several forum threads about PF100 house temp being 5 or so degrees different than the thermostat setting. The most successful fix I saw was putting some insulation foam between the wall and the thermostat case. I tried it and it fixed my 5 degree error too. It seemed to help keep the house temperature more consistent with the thermostat too. The thermostat reads the same as my digital room thermometer.

Thermostat2.jpg
 
This isn't PF100 only related.

Some things to consider when mounting thermostats and their cousins on a wall.

Never mount them on an outside wall.

Keep them away from drafts and things that can be opened and closed.

Make sure you place them where they get decent air flow.

Otherwise they don't really measure the general room air temperature.
 
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