Thermostat/aquastat help

Well I'm still stumped with my thermostat. The boiler has a Honeywell L8124 triple aquastat attached to it. It turns the stoker motor on when the boiler water temperature is below a certain set point and shuts it off when the water warms up. When the thermostat is calling for heat it turns the circulator pump on. The circulated water flows through a water-air heat exchanger located on top of my gas furnace. I want it to turn my forced air fan on as well. I have the Honeywell diagram but I don't see a 24v output, just the line voltage outputs for the circulator and for the stoker. If there is a 24v output I could run that to the "G" wire on the circuit board, no? If not I was thinking I could disconnect the furnace fan from the circuit board and hook one wire directly to the circulator pump's hot wire? I've done everything else myself up to this point, I'd hate to have to pay an electrician $100 to hook up 4 wires or so. I had the boiler going pretty good and had the thermostat terminals jumpered so the circulator was running and the forced air furnace fan wouldn't kick on until the gas burner ran through it's cycle, including energizing the exhaust blower fan and firing the gas burner.

You connected the thermostat to the coal boiler?

I envisioned something different.
Thermostat still on service furnace.
Start coal boiler, at minimum setting jumpered circulator starts. When hot water warms plenum enough, temperature switch should make preventing service furnace from firing. House thermostat calls for heat, service furnace fan blows. If coal boiler falls below minimum temperature, circulator drops out, plenum cools, service furnace takes over. It is totally automated that way. When you light a fire and get up to heat in the coal boiler, it will take over automatically. When the fire goes out, it will fall back on your furnace. The trick is making the plenum temp switch work properly. You may have to place it against the coil to get it to respond properly, or change the type of switch you are using.

That's what I had envisioned originally. It doesn't work. With the thermostat jumpered on the aquastat and the regular fiurnace set for a call for heat the circulator comes on at the set point and heats up the plenum heat exchanger but the gas burner also fires up. The heat sensing switch has to be down low because it doesn't close the connection. To make matters worse I don't know what it looks like. The other problem is for summer hot-water only use the circ. runs like there is a call for heat, but I probably could just un-jumper the t-stat connection for the summer or put a switch on the jumper lead.

e.alleg wrote:put a switch on the jumper lead.

A toggle switch right on the Aquastat would do it.

Maybe a relay? When the circulator starts, it would close the temp switch circuit.

I remember looking for a wiring diagram for your furnace on the web and couldn't find it. If you have one could you post it?

http://www.efmheating.com/manuals/DF520%20Manual.pdf

this is the EFM manual with the wiring schematic. Yanche posted the Honeywell info a while back, I'll see if I can find it in here.

We need the furnace wiring to run your blower, I have the EFM stuff.

http://www.nordyne.com/Literature/708291b.pdf full manual
http://www.nordyne.com/Literature/710184.pdf wiring diagram

Model: Tappan G6RA (144) upflow. (elevation 2300ft.)

I'm pretty sure mine has a single speed fan as there are just 2 wires coming off the fan.

Thanks!

In the electrical drawing it shows a blue wire circuit to 3 switches on pins 3 & 8 in the control box. The supply air limit switch is the one you are after I believe. I would disconnect one of those wires at the pin and see if the fan runs on the thermostat's call for heat. You will need to return the thermostat wires to your hot air furnace for this. If the blower runs, get a temperature switch (adjustable and closed in its cold state) that opens around 150* and strap it to the hot water feed to the coil and wire it to the blue wire loop. When the coil is fed hot water, it will tell the burner not to start as there is sufficient temperature at the plenum. The adjustable switch will allow you to fine tune your switch to the temperatures your unit sees in real time, watch it cycle many times to prove it repeats properly.

Problem solved for $12. and an hours time. My local hardware store was running a special; heat only thermostats for $5.99 . I used one to control the coal boiler, set that at 65 degrees. Used another one to control the furnace fan, set that at 65 degrees. The third one (original one) is set at 55 and will turn on the propane furnace as a backup in case I'm gone and the coal fire goes out. (as long as I remember to turn the gas back on, it really felt great to shut off that valve ) I could have used a 2 stage t-stat or wired up switches and relays, but this way works best for me, each system has it's own manual control so I can play with the settings pretty easily. I let the fan run after the boiler shuts down to blow off the stored heat into the house, that's "free" heat. I might have to set them at different temps, we'll see.

err I didn't quite get it to my liking. I've got a HVAC expert going to give me a hand this week, I'll post the results. The problem is the boiler needs to warm up the coil for about 3 minutes before the fan kicks on otherwise it's playing catch-up trying to warm the cold coil with the fan working against it. Once the duct is warm (after about 3 minutes) it works great. When the boiler circulator shuts off the fan needs to run to blow off the residual heat. Doing this manually makes for an 80 degree house and some babysitting the t-stats, not to mention wasted coal. My furnace has a circuit board that controls the 4 speed blower motor so it can be done automatically, I am just not experienced enough to figure it out. I think a 2 stage t-stat will fix the problem but we'll see what my buddy says. Ideally on mild days the fan will run on low and control the circulator providing nice even heat and ventilation, when it gets colder the next speed should come on, and so on until it's cranking full blast on the coldest days. The catch is I want to keep the gas furnace fully operational as a backup when I go away for holidays or whatever. I know it can be done I just don't know how, even after studying the furnace diagrams. When someone invents a controller to integrate a boiler to a forced air furnace they will have a nice product to market to all the OWB people and folks like me.