# Humble Furnace - Problem with Thermostat



## packerchick (Mar 6, 2016)

My hubby and I bought a house this past summer and it's main heat source is a Humble wood furnace.  We have had nothing but problems with it, but can't afford to buy a new one right now.  We're also both new to wood burning furnaces, so bear with me.

The biggest problem we have is that the furnace will not turn off even though the thermostat inside the house is off.  We thought it might be the thermostat and replaced it, along with rewiring the whole thing, but it still won't shut off.  Even replaced the fan & limit switch.....no luck.

We think it might be the electrical box that the thermostat wires attach to...along with the main blower/fan and centrifugal blower.  It seems like a mess to me and I'm not even sure where the thermostat wires are supposed to be attached.  I tried attaching a photo of it, but I'm unable to do so.  Sigh.

If anyone can help us out we'd really appreciate it.


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## coaly (Mar 6, 2016)

Is this the furnace and control ?


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## packerchick (Mar 6, 2016)

It is similar.


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## packerchick (Mar 6, 2016)

This is the box.  Weird I can upload it from my iPod but not computer.  Sorry about that!


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## coaly (Mar 6, 2016)

OK, so the thermostat only controls induction fan, and the fan does not shut off. Correct?
Is there only 1 blower for fire or is there another blower for heat circulation that does not shut off?
I want to make sure when you say the furnace doesn't turn off, you are referring to the small blower that blows air into the firebox.


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## begreen (Mar 6, 2016)

The electrical box is probably just the transformer and a relay. Can you get a sharper close up of where the thermostat wires are connected. It looks like there is a letter or number for each screw. I am trying to read the labels but it's a bit too fuzzy. If it's hard to get a sharp picture, can you tell us what the top 2 and bottom 3 screws are labeled?


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## begreen (Mar 6, 2016)

Moving to the boiler room with the hope that someone recognizes this furnace. Will leave a link here.


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## packerchick (Mar 7, 2016)

The blower that pushes air into our house shuts on and off, but we're not able to regulate it with the thermostat that's in our house.  So it'll keep running and running until the fan & limit controller determines it's too hot...only then will it shut off.  The induction fan turns on and off OK with a switch that looks like one you'd use for a room light.

The only letters that are labeled by the screws are the upper left (R) and the lower left (W).  Of course the R screw had the white wire in it and the W screw had nothing.  So we put the red wire in the R screw and the white wire in the W screw.....still doesn't work.

Sorry for not being specific with my answers....like I said we're new to this whole wood burning stuff.  Thanks for your patience!


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## garmford (Mar 7, 2016)

If you look at the front of your furnace, the box that's mounted on the right side of the furnace towards the top I am assuming its your fan limit switch. That box houses a probe that goes into air space between the firebox and the sheet metal exterior of the furnace. When you start a fire and heat starts to build up in that air space, the blower that sends heat thru the duct work will turn on once the temperature reaches the high setting that the switch is set to. When that air cools down, say when your fire is near the end of its cycle, the fan will shut off when it hits the low setting. 
Assuming that your Humble is similar to the Clayton that I used to own, the thermostat on the wall controls the induction draft blower on the front of the furnace. If the tstat demands heat the draft blower will turn on which will add more air to the fire that will create more heat and will heat your house faster. (It will also burn your wood faster.) When the tstat is satisfied, the draft blower should shut off. It's a great tool to get the fire started, typically once my fire got underway I turned the draft blower off manually. 
The tstat on the wall will not turn the fan off that feeds your house with warm air as long as there's a fire in the box. Unless your towards the end of the burn cycle the fan will cycle on and off until you reload with wood or let the fire go out. This is a built in safety feature so the furnace doesn't overheat and crack. 
The best way to control the temperature of your house would be to portion the amount of wood you add to the fire box. More heat-more wood. Less heat-less wood. It's a big learning curve with every wood burning appliance out there. 
I hope you can make heads or tail of my rambling, I'm sure I've left something important out. Lol
Where in Wisconsin? I'm from the Hartford area.


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## begreen (Mar 7, 2016)

Connecting the thermostat wires to the R & W terminals is a reasonable guess. I would take a voltmeter next and check the transformer to make sure you have 24vac (if it is a typical hvac transformer) out of the transformer. If not, the transformer needs replacing. If there is 24vac at the transformer then the next suspect is the relay.


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## begreen (Mar 7, 2016)

Connecting the thermostat wires to the R & W terminals is a reasonable guess. I would take a voltmeter next and check the transformer to make sure you have 24vac (if it is a typical hvac transformer) out of the transformer. If not, the transformer needs replacing. If there is 24vac at the transformer then the next suspect is the relay.


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## coaly (Mar 7, 2016)

As garmford stated, the thermostat only controls the air induction fan. On a call for heat it kicks up the fire which burns very low without the air induction fan force feeding the fire.

The limit switch is a switch normally closed (or ON to pass current) this allows induction fan to run unless it is in an overheat condition which should turn the induction fan OFF. This is in case the circulating blower fan fails and temperatures get dangerously high. A limit switch always limits the fire or heat output.
Limit switch is Normally ON and turns OFF on temperature RISE.

The circulation fan or blower is a separate circuit that has a fan switch normally OFF until heated when it turns ON to make contact through switch causing blower to run. It is not wired to thermostat, the heat from furnace affects the fan switch to control the house circulation blower.
Fan switch is normally OFF and turns ON with temperature RISE.

The circuit for circulator fan is simple being all 110 volt.

The circuit for induction fan is more complicated since the switch is a thermostat which gets its power from a step down transformer. This low voltage goes through the thermostat when points are closed calling for heat. The low voltage (normally 24 volts) energizes a relay which is an electrically operated switch that connects the high voltage (110v) to induction fan motor. Remember this voltage also goes through the limit switch before powering induction fan motor. So the thermostat controls the induction fan and the limit switch can shut it off as well.

Those basics are not only wood and coal burners. That is the basics that control oil, gas or electric furnaces. Controls are called different things like "primary control" for oil burner or aquastat for water filled boiler. The basic principals are the same.


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## maple1 (Mar 8, 2016)

packerchick said:


> The blower that pushes air into our house shuts on and off, but we're not able to regulate it with the thermostat that's in our house.  So it'll keep running and running until the fan & limit controller determines it's too hot...only then will it shut off.  The induction fan turns on and off OK with a switch that looks like one you'd use for a room light.
> 
> The only letters that are labeled by the screws are the upper left (R) and the lower left (W).  Of course the R screw had the white wire in it and the W screw had nothing.  So we put the red wire in the R screw and the white wire in the W screw.....still doesn't work.
> 
> Sorry for not being specific with my answers....like I said we're new to this whole wood burning stuff.  Thanks for your patience!


 
I'm not really experienced with hot air furnaces - but sounds to me from some stuff said here you should get a pro in to check things over. Before damage is done.

*So it'll keep running and running until the fan & limit controller determines it's too hot...only then will it shut off. *

If the furnace is hot, the circulation blower should not stop.

*The induction fan turns on and off OK with a switch that looks like one you'd use for a room light.*

The induction fan should be controlled by the thermostat.


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