Enviro Mini - had to short out exhaust sensor

[rsplodge]

Hi:

I just bought a used Enviro Mini pellet stove. I've been testing it outside before taking it to my cottage to install. I found that if I turned the stove on, that it would start and run, but after about 15 minutes it turns off. Note, I'm running it in "manual mode". The status light never stopped flashing and it did not hand over control to me to allow me to set the heat output. I took my DVM out and probed the exhaust sensor and this sensor always showed about 5V (when wires were attached). I removed the wires and shorted them out (as per some hints I had seen in a service manual) and then the stove would work and stay on. The convection blower starts up when I short out the sensor and the status light will go out at some point within 15mins of starting and allow me to set the heat output.
My question is whether this is due to the stove being outside, so perhaps the internal exhaust pipe never gets hot enough, which maybe is required during part of the stated 10-15 minute startup sequence. Or perhaps the sensor itself is shot. It does seem like the sensor keeps reading a very high resistance (DVM was on Auto and I don't think it ever showed anything other than overload/open) even after it's run a while. The person who sold it said the stove was running fine last year when they removed it to switch to gas, but he could be feeding me a line. I was surprised to see that he had enclosed a couple of receipts and he had paid about $500 in various service and parts costs, as recently as last year. I would have expected a pellet stove to be more reliable than that. I only paid $450 for the stove so I think I got a pretty good deal. If the issue is just a bad sensor then it won't be very expensive for me to repair, but I just want to make sure it's not just because I'm trying to run it outside for testing purposes.

Thanks, ...Roger

 

[JRemington]

Are you sure you aren't talking about the low limit switch. Some call it the proof of fire switch. By exhaust sensor do you mean the vacuum switch?

 

[rsplodge]

Are you sure you aren't talking about the low limit switch. Some call it the proof of fire switch. By exhaust sensor do you mean the vacuum switch?

I'm not sure what it's called. Yes I have seen reference to a low limit switch in posts but not in my manual. It is a sensor located right on the exhaust. Here is pic from the technical manual and pics of what I did. I'm color blind but I think the wires are brown. This means it is the Exhaust Temp Sensor. On another page it looks like they might call it the 120F Ceramic Fan Temp Sensor.

Note the back of the exhaust looks like that because the stove came without an exhaust starter tube/pipe which I need to purchase still.

 

[Ssyko]

The part you have circled is a low limit snap disc. It is an open circuit when the stove is cold. When it is started up and air temp rises to 120 deg a spring disc inside closes the circuit and alows auger to run and stove to go into normal operation. If you have jumped this switch and the stove runs then replace that switch and you will be up and running

 

[JRemington]

Ssyko is correct. If your stove doesn't reach 120 degrees in 15 min the switch will not close and the stove shuts off. When you jumped it it became closed and turned on the convection fan and gave you control over the stove.

 

[johneh]

I have also found that the switch can be covered in ash (underside) . The ash
will insulate the switch to the point where it will not read correctly
Remove it and clean may save you the cost of a switch
The Mini is a work horse easy to repair and clean
If you need help with any thing about the stove PM me
I live just outside Ottawa

 

[rsplodge]

I have also found that the switch can be covered in ash (underside) . The ash
will insulate the switch to the point where it will not read correctly
Remove it and clean may save you the cost of a switch
The Mini is a work horse easy to repair and clean
If you need help with any thing about the stove PM me
I live just outside Ottawa

Well thanks everyone. Ok that was my guess but I was just using the name of the switch from the manual.
Is it not possible though that it is not heating up enough because the stove is outside? Anyway I will definitely remove it and try cleaning it and also measure its resistance while heating it up. I will replace if it seems bad. It certainly looks easy to service.
Johneh, I might be in contact. Neat that you are near Ottawa.
The next thing I need is the starter exhaust pipe and I see one on eBay. Pretty pricey for a short piece of pipe with a flange though.

 

[Ssyko]

It wont have resistance so to speak, its an on or off switch, nothing inbetween. To test put your leads on the blades, set to ohms, heat the metal face and it will clic and you will see a completed circuit. As for testing outside if your in the open and in cold air its possible it could affect it. But i doubt it if it has a decent fire.

 

[rsplodge]

It wont have resistance so to speak, its an on or off switch, nothing inbetween. To test put your leads on the blades, set to ohms, heat the metal face and it will clic and you will see a completed circuit. As for testing outside if your in the open and in cold air its possible it could affect it. But i doubt it if it has a decent fire.

Oh ok that's what you mean by snap disk. Either open or closed. That explains why it was off the scale when measuring resistance!!
So is this the same though as the exhaust temp sensor that is shown in the manual pic I shared?

 

[Ssyko]

Yes, mfg’s love using large terms for simple item lol

 

[JRemington]

The switch is a normally open switch. It closes upon reaching 120 degrees during the startup cycle. The high limit switch on the other hand is a normally closed switch and when it opens it shuts the stove down.

 

[Mt Bob]

No exhaust adapter,no flue pipe,running outside, is entirely possible nothing wrong with switch.If you keep stove,you will need to find the year,as the early ones had poor burning problems,but there are upgrades to make it fine.

 

[rsplodge]

No exhaust adapter,no flue pipe,running outside, is entirely possible nothing wrong with switch.If you keep stove,you will need to find the year,as the early ones had poor burning problems,but there are upgrades to make it fine.

Nah, I brought the part into work today and heated it up to 250F and it didn't close so I guess it needs replacing. Ok, thanks for the advice about upgrades. I do see on these forums that they came out with an "A" model, and I saw the thread that mentioned the differences.

...Roger