I just installed a Honeywell focus pro 6000 programmable thermostat I have a boiler with a indirect hotwater tank and a taco sr502 switching relay.. On thermostat I wire red to r white to w and blue to c. On switching relay I wire white to on left termial and red to right termial which I had the old one working on also hooke up the blue to the common side of the 24 volt on the taco 502 . Problem is I still need the batteries installed if I take the batteries out it doesn't light up . Does this thermostat require the batteries to be in place? It says either or in manual.. thanks for any help it is a heat only system now..
Guysr1

I solved it myself all I had to do was switch the red and white from thermostat to where the white was on taco zone 1 tt left side was white right side was red . Now left termial is red and right terminal is white simple but frustrating to figure out
Now don't need batteries.. can use for backup still.