Taco sr503 relay question

Leon82

I'm only using zone 1 and 2 and the tt contact goes to the first tt input on the boiler.

I want to move the 2nd zone to the priority zone 3 and use the priority tt to the second tt input on the boiler to run a separate odr/temp curve. But I want the priority function inactive

I read the directions a few times and am a little confused. Do both end switch close when the priority zone calls for heat? If so it is going to kill my plan

Thanks

Dave H_2

It sounds like you have a SR503-EXP? Am i correct?

The -EXP controllers have two separate end switches (XX). The "Main End Switch" only closes upon a heat call from any heating zone, in your case Zone 1 and Zone 2.

The "Priority End Switch" only closes when Zone 3, the priority zone, is calling for heat as long as the priority switch is on.

Dave H.

Leon82

Yes , exp.
Thanks

Leon82

It looks like it won't work like I had hoped.

I'm getting 7 volts across rw on a the zones NOT calling for heat. Is this normal?

It is a battery thermostat with only 2 wires

HVACNUT

When the thermostat is open, it should read 24v across TT for that zone because it's kind of a false reading as it's picking up voltage through the relay coil.
When the thermostat is closed, it should read 0v across TT

Leon82

Ok, thanks. The one that's closed is at zero currently