Both of you have been a great asset in helping me learn how the aqua stat and relays work. With your advice, looking at other set ups, the wiring diagram in the EFM manual (why didn’t I think to look there!!!), and measuring the voltage on the terminals when the relays kick on/off, I was able to get a pretty good handle on this.
I have the coal boiler and oil boiler set up as individual units (separated by ball valves). This allows me to completely shut down one of the units and run the other. They share circulators, thermostats, and the piping distribution system. Each unit has its own L8124A Triple Aqua stat relay on it. I assume that is why the plumber ran each thermostat (one for the first floor, and one for the 2nd floor) to the two R845A relays (basically this was the easiest way for him to do it!). If he would have wired the thermostat to the aqua stat and used the C1 C2 terminals to feed the circulator it would not have worked when I shut that unit down and turned on the other unit. The problem is the R845A's are just relays and turn the circulator on when the T-stat calls for heat and will run until it’s satisfied. They don’t give me the benefit of the L8124A Triple Aqua stat relay, by starting the stoker when the T-stat calls for heat, or by shutting down the circulator when the low limit is reached. I have a tank-less hot water coil in each unit. You can imagine when the low limit is reached on the coal burner, and the circulator keeps running the water through the system, that it takes a great amount of time to bring the boiler back to temperature and it’s difficult to maintain a decent domestic hot water supply. I think by having the stoker start as soon as the T-stat calls for heat, and shut down on the low limit, I should be in pretty good shape.
I’m thinking if I run the thermostat wires to a double pole double throw switch (on-off-on), it would allow me to choose which aqua stat is being controlled by the thermostat. Since I already have to close and open valves, as well as main power when I change from one unit to the other, it would not be a big deal to also throw the switch to control the thermostat.
The question I have now is how to connect the C1 and C2 from each aqua stat to the circulator. If I just use a junction box and connected both C1’s to the hot wire of the circulator, and both C2’s to the neutral of the circulator it would allow power from the aqua stat that is currently being used to power the circulator. [u]The only issue is that the junction would also put power onto the C1 C2 terminals of the aqua stat that is not being used. Since I wouldn’t have any AC power going to the input of that aqua stat, would it be a problem to basically be “back feeding” the AC onto those terminals? [/u] If so, I guess I could get a single pole, double throw switch to isolate the voltage and only send the AC from the aqua stat being used to the circulator, and isolating the other aqua stat from that voltage.
I want to keep the number of switches and ball valves that must be “thrown” to a minimum. I know I will be able to understand it, but if I die my wife will never figure it out!!!
I guess the real question here is if it’s a problem to have AC on the C1 C2 terminals of the unused (and unpowered) aqua stat?
Thanks for any input.