Harman ESP and, aging fan speed?

[Mac McIlvaine]

I have over the years replaced a few of the ESP units on my Harman.

What exactly is in the thing? It doesn't act like a thermocouple when measured. The old one I just replaced is around 200k ohms at room temp and goes down as the temp goes up. The new one reads about 600k and goes down with temp increase. (others I've replaced were just open circuits)

My first guess was a thermocouple since that's typically what would be chosen for high temp nasty environs.

Any ideas?

Also, was told the ESP units can fail if the draft blower slows with age. Is this correct? (Do they just fail or actually go slower with age?)

Regards,
Mac

 

[johninwi]

I believe they are thermisters, the older one's at least like you have, black wire's right? The newer have red wire's and start around 1k and go up when heated.

Welcome too.

What do you have for a stove and it's age if you've gone thru multiple esp's? I'm still on the oem parts at 4 years without problems. As for a motor slowing with age? I'd ask for a few more details on that statment.

 

[Mac McIlvaine]

Black wires yes, now. The first one was red and was replaced (with a red ) under warranty the first year. The 3rd was black and just replaced with black.

It's a P43 and this is the 5th season.

I'm pretty skeptical of the "aging motor" theory as well...

 

[Mac McIlvaine]

I wonder about the ESP being a thermistor. Run other mill thermistors typically don't go much above 100C. Though there are expensive industrial models that will handle 300C.

 

[Harman Lover 007]

My Harman Invincible is 18 years old and I've never replaced the ESP.

 

[F4jock]

My Harman Invincible is 18 years old and I've never replaced the ESP.

Mine's six and all I've done is clean it yearly. When you went from red to black etc. did you change dip switch 5?

 

[ironpony]

My Harman Invincible is 18 years old and I've never replaced the ESP.

Mine too. 1 combustion fan last year, otherwise set it and forget it.

 

[Mac McIlvaine]

Ok, so I do a basic clean out every time I empty the ash bin and every other week or so scrape down the innerds. Then a full clean out and the end of the season.

So what am I doing that is killing the sensors?

In the third season I had a bad burn issue that caused a lot of creosote buildup and toasted the sensor. But that has not been an issue since.

I do see spark streamers from the burn pot when it's running, but the ash looks normal.

It's plumbed into a stainless chimney liner. Is draft a possible issue? Too much/little?

 

[johninwi]

It's plumbed into a stainless chimney liner. Is draft a possible issue? Too much/little?

I have 23' of 4" liner in a chimney that has insulation stuffed around the top and a plate above that, i can still access inside the chimney at the bottom and it's quite warm so i believe i have a descent natural draft, I've also reduced my draft adjustment as far as it can and will only see smoke at start up. Based on the lack of smoke i believe my air flow is fine.
Most everyone here is direct vent straight out or out and up a short way.
Yep, all that info just to say i doupt your liner is part of the issue.

So what am I doing that is killing the sensors?

a good question, lots of power outages in your area? I'd expect that to be harder on control boards than esp's thou.

What do you clean the esp's with? Mine i'll brush with a paint brush most times (1" paint brush on a stick and i can reach it thru the exhaust inlet) and occasionally a paper towel, recently i used fine steel wool, thats about it.

 

[Mac McIlvaine]

I can understand how crud on the sensor could effect the sensing.

But I'd expect it to go bad because of being exposed to temperatures that would fry the probe element or corrosion through the metal of the probe and destroying the element. Other than the one in the creosote buildup fire they did not show this sort of damage. Those that were bad just were now in the wrong resistance range.

We do have power outages...but I have a whole house generator. And whole house surge protectors.

 

[johninwi]

When my esp is cruded up i'll get less heat from the stove, i would guess the crud insulates the sensor.

But I'd expect it to go bad because of being exposed to temperatures that would fry the probe element or corrosion through the metal of the probe and destroying the element

I've been reading this site for about 4 years and don't recall posts of others losing esp's with this frequency, so what is different in your setup?
The esp's you've removed, did they look any different than the new one's. Mine has a faint yellowish tint from the heating.
Liner sze 6" or 8"? left over from a previous wood stove and causing wierd air currents that rapidly cool the esp? Thermo shocking it? Using chemical's to clean the glass and corroding the esp?
Just thinking out loud..

 

[Bkins]

Also how are you cleaning your ESP when you do clean it? I've never replaced on either and was told the one in my insert was original to the stove. So around 20 years of use and it's still going. We are not using it as much this year as we changed over from oil to gas heat and are now really only using one stove to keep our family room at 76. Nice, very nice.

 

[Mac McIlvaine]

Liner was purchased with stove, recommended by the harman dealer. I suppose running it in room temp mode would shock the sensor regularly. I do clean the glass, but there would only be trace remnants of the cleaner once the door is put back on the stove.

I could see how low combustion ait flow could allow it to over heat . But I'd expect the controller to reduce feed and try to shut down if the stove was going past set point.

Does your sensor sit basically centered in the exhuast, mine tends to hug the side of
pipe.