My furnace doesn't turn off

[denno1]

Greetings
Problem in general: my (biomass) furnace needs the thermostat to be set to start up, but, once going, it doesn't shut off when the set temperature is reached or the thermostat turned down.
NB: This was a tiny company, "Superior," and it is gone. Was about 4 people. Can't consult them
I have already changed the thermostat (including the wires.)
This is a 4-5 year old furnace; problem developed sometime last year.

Here is the process of running the furnace.

1. start a fire manually in the firepot. Set the switch at "Start" [This switch has Run, Off, and Start. It controls the blower in the firepot, and the augurs that bring corn and pellets from the bin to the pot.]

2. the pot blowers go on and the augurs start. First of all, and this either is or is not a correct memory, I think maybe the augurs were supposed to wait until a certain heat level was reached just in the pot. I think they maybe start right with the switch now.

3. (used to be) augurs start up.

4. after 10-20 minutes the house blower starts and we start getting heat. At this point, the switch ought to be turned to Run. Thereafter, the pot blower and augurs should run on demand from the thermostat. When the desired temp is reached, those go off and a timer is engaged which runs a cycle of 3 min on and 7 min off----equivalent of a pilot light.
(The house blower continues to run even when the 3-way switch --- but not the system power switch --- is turned off, until the temperature drops sufficiently.)

5. Resetting the thermostat higher should fire up the furnace until that temp is reached (unless it can't be; in which case it keeps trying.)

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I have found lately that when I start the furnace up, the house blower does not start until I have turned the thermostat up. However, it does not go off if I turn the thermostat down.

Parts to this elec system......thermostat, limit switch, 3-way switch, system power switch, timer. If there's more to it, y'all may have to tell me what to look for.

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I have some limited ability [and dexterity and limberness (!]) to put a multimeter on things; but no wiring diagram.

I am hoping my description of the system's behavior will define what part of it must not be working right.

Thanks for your presumed attention to this matter. As they say.

denno1

 

[Wilko]

Hi - sorry to hear that your heating is playing up. If I was nearby (!!!) I’d enjoy helping you on site to draw a system diagram and diagnose the fault. If the house blower is no longer turning off when the thermostat is turned off what does stop it? There will likely be a contactor that is controlling the blower and it may have failed. But I’d have to say that’s a wild guess without some sort of system wiring diagram. And so the risk becomes that without understanding how it is supposed to work we end up playing “spare parts roulette”.

 

[StephenRowley]

What's the make and model of the boiler?

The manual for the boiler would be the starting point.

 

[denno1]

OK, thanks for quick interest.
As noted, it's a Superior Corn Furnace, no available make, model, or diagrams. Was a TINY independent company, now defunct (as are probably the 3 or 4 principles.)

Correction: the house blower still goes on and off according to whether the firepot is cooled off enough or not.
It is the augurs and firepot blower---the heat producing part of the operation---that does not shut off with the thermostat. What shuts them off is either that 3-position switch ("Off") or the main system power switch. (Or the breaker, same thing in effect.)

My analysis, I g-u-e-s-s, is that whatever sensor should report that the set house temperature has been attained is not telling the pot part of the circuits to take a rest. So----signal from the thermostat possibly reaching but not operating the part of the switching system that goes from "Run" to "Timer Cycle." Reminding you that the timer cycle is the 3 min on 7 min off resting state that keeps the fire "banked" without needing to be relit.

It is possible, maybe, I can i.d. the components and that they have their own circuit diagrams online.

But, to reiterate another way for myself, say the signal from the (new) thermostat goes down to the switching widget but inside the latter does not make its way to telling the system to make a change.

Confused (or clarified?) by the thermostat's having to call for heat to begin producing heat when the furnace is first lit----otherwise the house blower doesn't come on.

[I guess this is at odds with the idea that the house blower operates in a separate way to keep the firepot from overheating. Perhaps I need to observe this some more....]

This help sort it out any?
If I had to take a shot in the dark at fixing things, I guess I would
A) replace that switchwidget or
B) call our rather good electrician

denno1
I'd just go by denno but the forum makes me use 6 digits!

Oh, dang----is there a way to UPLOAD pix from the computer, as opposed to LINK to ones online?

 

[denno1]

I found a copy of my copy of the manual!
Includes wiring diagram. Now I'll have to see if I can read one...

I hope this will lead to it: https://www.teksupply.com/wcsstore/...llbizunits/techdocs/SUPERIOR CORN FURNACE.pdf