Combustion motor won't turn off on Harman P68

[Dale K]

The combustion motor on my Harman P68 won't turn off after the stove cools down when I turn the control dial to off. The first time that this happened was when I let the stove run out of pellets when we left home for a few days. When we came home, the combustion motor was still running. Anyone have any thoughts on what's wrong and/or how to correct?

 

[TimfromMA]

Possible POF switch. The stove may think theres still a fire going in the burnpot.

 

[Bioburner]

Harman has no proof of fire but a what they call an "ESP" in the exhaust path behind the exhaust fan.(fancy thermal probe)Seems to be a cause of stove not shutting down an another cause is the pot switch that controls the fan and on off functions.
ESP can be damaged when cleaning. How old of stove?

 

[mikesj]

If the stove is clean and otherwise working ok, then I would look at the esp. Remove and clean it- it only takes a minute or two. If it still isn't shutting down replace it. They go bad every now and then.

 

[kelly]

If the stove is clean and otherwise working ok, then I would look at the esp. Remove and clean it- it only takes a minute or two. If it still isn't shutting down replace it. They go bad every now and then.

I Just went through a similar problem with my p61 and I second the thought of ESP , Bioburner asked for year of stove for some history and if its got some years on it . I second the ESP though , it will have a black wire or a red depending on year and the screw for removing is a 1/4 and suggest as well clean first then see how it burns and shuts down

 

[Dale K]

If the stove is clean and otherwise working ok, then I would look at the esp. Remove and clean it- it only takes a minute or two. If it still isn't shutting down replace it. They go bad every now and then.

Thanks. I'll try this first. This is my seventh winter with this stove. Works great. I clean it regularly. First time that I've had this problem.

 

[newf lover]

That happened to me and it was the control board.

 

[kelly]

That happened to me and it was the control board.

sorry to hear that . Harman is a very solid product , and lets start with the basics ESP cleaning and then run it , if the cleaning doesn't cure the problem , replace ESP with the correct colour and then run , I suspect that will very likely be the problem , there is a way to check with a diagnostic tool - Harman tech has and it will look at the ESP while running . From what I understand the ESP probe measures heat and sends a voltage signal to the panel and translates the voltage signal as a temp , and allows the stove to know how its burning and the temp of the exhaust , as these probes go bad it is telling a incorrect voltage telling the stove its still warm continue clearing the burn pot with the combustion fan and the probe just has gone bad . You can measure the ohms with a voltmeter when at 70* and it should be a certain ohm reading but im not the guy to tell you the range it should be , there are men on here that know and may chime in but I believe one has already stated clean the probe and try then replace - they are inexpensive and probably the cause . These machines are not known for board problems but without a surge protector inline you can look to a power outage as a surge that can take out small boards like these . frequency that have have seen states clean and or replace the probe - basics first

 

[Dale K]

sorry to hear that . Harman is a very solid product , and lets start with the basics ESP cleaning and then run it , if the cleaning doesn't cure the problem , replace ESP with the correct colour and then run , I suspect that will very likely be the problem , there is a way to check with a diagnostic tool - Harman tech has and it will look at the ESP while running . From what I understand the ESP probe measures heat and sends a voltage signal to the panel and translates the voltage signal as a temp , and allows the stove to know how its burning and the temp of the exhaust , as these probes go bad it is telling a incorrect voltage telling the stove its still warm continue clearing the burn pot with the combustion fan and the probe just has gone bad . You can measure the ohms with a voltmeter when at 70* and it should be a certain ohm reading but im not the guy to tell you the range it should be , there are men on here that know and may chime in but I believe one has already stated clean the probe and try then replace - they are inexpensive and probably the cause . These machines are not known for board problems but without a surge protector inline you can look to a power outage as a surge that can take out small boards like these . frequency that have have seen states clean and or replace the probe - basics first

My dealer let me use his diagnostic device which showed me that the ESP probe temp wouldn't go below 117 degrees F thus telling the control to keep the combustion fan running. I installed a new ESP probe (probe cost $70) and it fixed the problem. Using the diagnostic device, I saw that as the stove cooled down after being shut off, the distribution fan turned off at 130 degrees and the combustion fan turned off at 90 degrees. There was no visible damaged to the original ESP probe.

 

[johninwi]

Dale, if you have an ohm meter could you check the resistance thru the damaged esp? Perhaps compare to the new esp also?
Would be helpful for future trouble shooting for others.
Also, red or black wires?

 

[Bioburner]

My dealer let me use his diagnostic device which showed me that the ESP probe temp wouldn't go below 117 degrees F thus telling the control to keep the combustion fan running. I installed a new ESP probe (probe cost $70) and it fixed the problem. Using the diagnostic device, I saw that as the stove cooled down after being shut off, the distribution fan turned off at 130 degrees and the combustion fan turned off at 90 degrees. There was no visible damaged to the original ESP probe.

Thanks for letting us know the findings of temps that a new ESP is reading and controlling fans at temps.

 

[Dale K]

Dale, if you have an ohm meter could you check the resistance thru the damaged esp? Perhaps compare to the new esp also?
Would be helpful for future trouble shooting for others.
Also, red or black wires?

It has black wires. With my analog meter, the bad ESP is reading 200,000 ohms at room temp at the small plug that connects to the control board.

 

[fire451]

I don't know if this has anything to do with your stove, but my 52i will keep the exhaust fan running as long as the door is still open, when I'm cleaning the burn pot and the temperature is near the point of shutting down, I noticed as long as the door stays open the exhaust fan will continue to run. many times as soon as I close the door, the fan shuts down. just my 2 cents.

 

[kelly]

thanks glad to hear you accomplished the task , appreciate the reply back well done