Anthrastat shorting out?

Seems my anthrastat went bad. I had a problem when I originally hooked everything up. I found a simple fix where one of the wires inside the anthrastat were they are soldered to it was touching the housing. Now today while I was leveling the coal bin out I heard some noise and the furnace blew the breaker. Once again I isolated it to the anthrastat. It seems like a fairly simple device. I can only assume it’s from within the little black box. Anyone else have a similar problem? I’ve been waiting on another anthrastat for months now.

The Anthrastat is a very simple device. It is a Bi-metallic rod that activates a snap switch. Chances are that you just need to replace the wires inside. The insulation may have come apart due to heat and age. That would cause a short if one of the wires contacts the housing. Both wires carry 120 VAC.

-Don

I think you can get by without it if the ashing ratchet is set at the right speed and isn't too fast.

Here’s where it gets interesting. I pulled it apart wired it in and it was fine. I even held the switch in to see if it caused a problem then. I can’t find any wire without good insulation. The last thing I’m gonna do is wrap all the wires in electric tape then put it together to see if it’s a short inside the switch because it is a metal plunger that sits again a metal plate and all of that is attached to metal and the furnace. Every other part of the anthrastat is mechanical.

I managed to get it back online. I have the switch fully insulated with a layer of electrical tape. Might be throwing the calibration off slightly.

I think you have the right idea there Egg! Check that the insulating paper is still in there and hasn't rotted off or burned through.

Anthrastat anatomy,

The Anthrastat is a Bi-metallic rod that activates a snap switch. The tension on the snap switch is adjustable via the ashing temperature screw. Remove these 2 large screws to remove the cover. Pull the cover off. There should be heavy insulating paper between the terminals of the micro switch and the cover. This reduces the possibility of shorting to the case. Insulating paper removed. The 2 wires connect the micro switch to the terminal block. The snap switch is a piece of spring steel mounted in such a way that it will quickly "snap" back and forth as an over center spring. Adjustment screw is attached to the Anthrastat knob. The top screw just holds the spring. The reason for the "snap" is to reduce the time that the switch contacts stay in close proximity to each other. This in turn reduces arcing across the switch contacts due to the high voltages involved and prolongs the life of the micro switch.

The micro switch is the small black box on the right. -Don

I just ordered a new switch. Someone on eBay is selling them. Kinda salty but the numbers and make match. Not that cost really matters anymore because I’m still waiting on a new anthrastat from axeman. Going on 4 months now.

StokerDon wrote: ↑

Thu. Dec. 26, 2019 12:42 pm

I think you have the right idea there Egg! Check that the insulating paper is still in there and hasn't rotted off or burned through.

Anthrastat anatomy,

The Anthrastat is a Bi-metallic rod that activates a snap switch. The tension on the snap switch is adjustable via the ashing temperature screw.

Remove these 2 large screws to remove the cover.

Pull the cover off. There should be heavy insulating paper between the terminals of the micro switch and the cover. This reduces the possibility of shorting to the case.

Insulating paper removed. The 2 wires connect the micro switch to the terminal block.

The snap switch is a piece of spring steel mounted in such a way that it will quickly "snap" back and forth as an over center spring. Adjustment screw is attached to the Anthrastat knob. The top screw just holds the spring.

The reason for the "snap" is to reduce the time that the switch contacts stay in close proximity to each other. This in turn reduces arcing across the switch contacts due to the high voltages involved and prolongs the life of the micro switch.

The micro switch is the small black box on the right.
-Don

Thanks don. I checked everything and it really seems like the switch. I could be wrong. I insulated everything and it’s working again.

My guess is that you fixed it by insulating the terminals better. If anything goes wrong inside the micro switch it won't work at all anymore.

-Don

StokerDon wrote: ↑

Thu. Dec. 26, 2019 1:02 pm

My guess is that you fixed it by insulating the terminals better. If anything goes wrong inside the micro switch it won't work at all anymore.

-Don

Good possibility. I don’t know the internals of the micro switch. Figured it won’t hurt to have a spare. I can’t see how any of the mechanical parts would go bad. As long as it has taken to get a spare anthrastat I figured it might be a good thing to have some spare parts for the one I have either way.

While we are on the subject has anyone pulled the actual probe apart? To me it looks like a stainless steel tube with a steel rod fixed in place at one end. Does it work off of the expansion of the inner rod when heated?

I have never taken the probe apart. It is a covered Bi-metallic rod. Yes, Bi-metallic rods expand with heat. Wait, it might be the other way. That is what pushes the snap switch.

I don't know what a new Anthrastat costs but I'm sure it's not cheap. I have 2 good ones but I have been running the snap switch section of an old Honeywell Aquastat for the past couple months. It has worked flawlessly. I haven't come up with a good excuse to switch back yet! The nice thing about this is it has an adjustable differential. I have it set at 5.

-Don

StokerDon wrote: ↑

Thu. Dec. 26, 2019 1:33 pm

I have never taken the probe apart. It is a covered Bi-metallic rod. Yes, Bi-metallic rods expand with heat. Wait, it might be the other way. That is what pushes the snap switch.

I don't know what a new Anthrastat costs but I'm sure it's not cheap. I have 2 good ones but I have been running the snap switch section of an old Honeywell Aquastat for the past couple months. It has worked flawlessly. I haven't come up with a good excuse to switch back yet!
IMG_5013.JPG
IMG_5014.JPG
IMG_5009.JPG
The nice thing about this is it has an adjustable differential. I have it set at 5.

-Don

Do you have any videos on that? Is that an aquastat? Does the copper tube have water in it? I’m very curious.

Ok my reading comprehension is terrible. I see it’s an old Honeywell aquastat. What would the modern equivalent be