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Taco SR504-EXP Boiler Relay help!

DoubleD629 Member Posts: 3
edited February 2020 in Gas Heating
I am looking to upgrade 3 Honeywell relays that control the hydronic circulator pumps on my boiler.
Pic 1.

The problem with the current setup is the need for a common wire to power my smart thermostats. The current setup is power robbing from one another and so I purchased a Taco SR504-EXP-4 which has a three wire setup for a common wire.
I have a Burnham Low pressure Gas Boiler with an aquastat that stays at a constant 210 degrees.
The current setup has 2 thermostats with an indirect domestic hot water heater w/aquastat for a total of 3 switching relays.

I am also confused about this 24v relay which is wired straight from the 3 Honeywell relays and then into the "TT" on boiler aquastat.
My guess is this relay sets priority to DHW circulator.
Pic 2

Does the Taco Board replace this 24 volt relay?

The boilers L1 and L2 wires are currently run to one of the Honeywell relays
and the "TT" is wired from the 24v relay.

The Taco board does not discuss anything regarding L1 an L2.
Pic 3

Aquastat photo.

Can anyone help?