Taco SR502, Thermostat, Circulator Help

consoleb

On my boiler I have a Taco SR502 Switch, there are three lights on the side of the switch, one for power, one for Zone 1, and the last for Zone 2.
On the boiler there are two circulators, one for a single loop to all the radiators on the first floor. After the first circulator is another identical circulator that goes to a loop around the basement that is unfinished (all the corners are missing the brass elbow). If you open the ball valve to this circulator water shoots out at the first corner. The previous home owner died before he could finish, I guess.
I have two rooms without heat so I installed radiant heat and bought a Caleffi Mixing station that has a manifold and a circulator.
Inside the SR502 on the circut board there are terminals for three thermostats, and three circulators each titled zone 1,2 or 3.
My existing heat is connected to zone 1 on both the thermostat and circulator. The second circulator is wired to the Zone 2 terminal on the Taco SR502 BUT there is no thermostat connected to the Zone 2 Thermostat terminal.
My questions are, 1. Do I connect the Caleffi Mixing Station Circulator to the Zone 3 terminal? 2. Do I connect the additional thermostat to the Zone 2 terminal to signal the 2nd boiler pump, or Zone 3 terminal of the Taco SR502 for the mixing station?
In most of the information I've read the boiler Circulator supplies the Mixing Station Circulator.
Thanks for any help.
Consoleb

SteveSan

If your SR502 is the old style ( metal cover ) we used the same "board" for both the SR502 & SR503 switching relay. You will notice there are only two relays on the SR502 and you would have 3 relays on the SR503 . You would only be able to use zones 1 & 2 and not zone 3 on the SR502. If you have any questions please contact Taco Tech Support 401-942-8000 Mon-Fri 8am-5pm EST.

HVACNUT

@SteveSan got you covered on the SR502.
I got a little confused on the zones.
Zone 1: main zone heat?
Zone 2: future radiant zone for the basement using the Caleffi mixing station?
Zone 2 used to be the basement zone but now its gonna be radiant?

consoleb

Thanks for clarifying, there are only two relays (if they are those similar to those in my car fuse box, little square boxes). Do I need a different switch if there is only going to be two zones but three circulators? Or do I just remove the 2nd pump from the boiler and connect the hot water directly to the Mixing station pump, and connect the mixing station pump to the zone two terminal on the SR502?
There will only be two zones the main house and the two rooms that have radiant floor heat.
Thanks and please give advice.
Brian

HVACNUT

The existing circ for Zone 2, basement gets removed.
The circulator for the mixing station gets wired to the now vacant Zone 2.

consoleb

Thank you. I'm going to wait until after this storm to do any work on the heating system but I couldn't do it with out help from you guys.
THANKS AGAIN
Brian