How to operate stoker and Circulator independently

When Thermostat calls for heat stoker operates with circulator, I know its anticipating heat .
I have radiant pex tubing with 120 water temp, boiler water temp could be at 190 and stills runs with circulator running
Do all the new efm boilers get set up this way. I could see a oil burner set up this way, but why a stoker . I would like to set up aqua stat to start stoker on the low limit and shut off on the high limit and let the circulator do its own thing ,is this possibly. I have a L7224 electronic aqua stat and a Taco 503 three zone switching relay My fourth zone is wired directly to aqua stat All the zones operate the same way with circulator
Thanks

How low do you want the temp to go before the stoker starts ? You should not see condensing temps or you will have rust problems. If you draw down the temp too low it may not recover quick enough. Is it only one zone you wish to do this to, then place that circulator on it's own relay, thermostat to relay tt, and the 120 out to the circulator and don't connect to the triple aquastat. It would not run from the low to high setpoint, but the low setpoint to the differential setpoint on the stokers triple aquastat.

What temperature water do you need to do the job on below zero days?

Assuming you don't need the stoker to run up to the high limit on cold days, put the forth zone on its own relay (or upgrade to a 4 zone controller), and wire it up without connecting the end switch to the aquastat. You will need to do the same to the existing zone controller. This will allow the circulators to run on a heat call regardless of boiler temperature, and the stoker won't start until the low limit is reached. The downside to this approach is that the circulators won't shut off at the low limit to protect the function of the tankless coil...if you use one that is. I'd have to study the wiring diagrams of the Taco control to see if you can get the best of both worlds.

I would like to go with 145 low 185 high The taco 503 has 3 zones the 4th zone goes only to aqua stat and the boiler also comes on with that circulator. The part I don’t like is the radiant is slow heat and the boiler temp goes to 195 and with mixing valve I only need 120-125 . I would only do this to the one zone coming from taco relay that’s the zone that drives up the temp . I don’t understand (end switch) “wire it up without connecting the end switch to the aqua stat” I do have hot water coil EFM 520 Thanks for your help and your time.I found wire diagram I don’t know if this helps
[http://www.taco-hvac.com/uploads/FileLibrary/102-167.pdf

cardinal wrote:When Thermostat calls for heat stoker operates with circulator, I know its anticipating heat .
I have radiant pex tubing with 120 water temp, boiler water temp could be at 190 and stills runs with circulator running
Do all the new efm boilers get set up this way. I could see a oil burner set up this way, but why a stoker . I would like to set up aqua stat to start stoker on the low limit and shut off on the high limit and let the circulator do its own thing ,is this possibly. I have a L7224 electronic aqua stat and a Taco 503 three zone switching relay My fourth zone is wired directly to aqua stat All the zones operate the same way with circulator
Thanks

It should operate the stoker on a temperature fall from the high limit only after it falls beyond the differential set point. The reason is on a long or multiple calls for heat, you may bring the boiler temp well below the low set point which would lock out your pump until the low set point is reached again. I would make sure your differential settings are correct and working properly before re engineering anything.

coaledsweat wrote:It should operate the stoker on a temperature fall from the high limit only after it falls beyond the differential set point.

The boiler should fire 10 below the high limit on call for heat, and 10 below the low with out a call for heat. The only thing the adjustable differential does it determine the amount of rise above the low limit. As far as 1 zone without firing the boiler, I would wire that zone to it's own relay,from thermostat to circulator and NOT to the triple aquastat. Then it would fire 10 degrees below the low limit and stop at whatever the adjustable differential is set to. The only thing to consider is when it hits the low limit, the pump will not stop and it could draw the heat down below the low limit till it makes a good bed of fire unless you add an aquastat to tell the pump to stop when it's to cold.

Thanks I will put that zone on it's own relay and ,add another aquastat. Any advice on relay model and number and aquastat model