honeywell multiple aquastat controller,wood boiler, wiring to control fan limit switch on low limit

[markmudd]

I have honeywell 4081B multiple aquastat controller on my 6150 royall indoor wood boiler. Previous owner of the unit used low limit side to control a separate circulator and dump zone.

The high side is fixed 10- degree differential and it works as it should, book says low limit is adjustable 10 to 25 degrees and is not presently hooked up.

I would like to use the low limit side of the aquastat to act as heat exch fan limit switch running to fan control center relay so fan will run only when boiler is up to temp and not run too long to reduce boiler temperature more than 10 or 15 degrees before shutting off.

I have read the book on the aquastat over and over and cannot find how to adjust the low limit differential. Book says it is adjustable 10 to 25 degrees.

Questions

1. Has anyone ever used this type of aquastat on low limit side be used to act as a fan limit switch thru the fan relay? If so can you provide wiring diagram so I don't cook this controller guessing how to do it.

2. Is there a way to mannually change adjust the low limit "differential" to around 15 or 20 degrees or is the differential adjustment based on how it is set compared to high limit setting? I'm obviously confused about the adjustable low limit "differential" and book is not making lots of sense to me.

I tried using the 110 Volt limit switch from my old forced air wood furnace mounted just over the heat exchanger. It works but is difficult to adjust because temp just above exchanger is not really indicative of water temp and adjustment is a frustrating guessing game plus differential at it's tightest is about 25 or 30 degrees.

By the way this royall indoor boiler really appears to be a good unit.

thanks

Mark

 

[markmudd]

I went ahead and ran a switchleg wire to my fan relay to the low limit sideof the aquastat and it appears to be working to control fan on/off based on temp. The instructions on it say to set low a min of 20 degrees below high limit. I did that and seems to be working as it should. Still not sure about the "adjustable differential" part of this unit and if I can manually change the differential between 10 and 25 degrees. if it is indeed adjustable, maybe you have to take it apart to get inside or to the backside of contoller? I guess I know just enough to be dangerous, but it appears to have worked. The Aquastat is more accurate than the hot air limit swich I had installed, I just have not had time to track to see how low the water temp will go before fan will not run.