Laars ft floor combi and taco 504 exp

Bbktrades

I have recently installed these two items.

The boiler and the taco are working together except for the Zc terminal.

When the CH is running and it calls for dhw, the laars is to put dhw as priority. It does this through the Zc terminal on the board.

I have the taco and the laars wired up as per the diagrams (attached).

The zc on the laars has 120v (to Com) when the CH calls for heat. And when dhw calls the voltage on ZC drops to 30v.

On the taco side it doesn't do anything with the change of the voltage of ZC. (all dips switches off)

When I turn the zc dipswitxh on it shuts the zones off immediately (regardless of the zc voltage) and the zones don't come back on unless I flip the zc dipswitxh off.

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EdTheHeaterMan

The Taco SR504 EXP-4 is not the control you need. The Taco SR 504-4 is all you need. That said, You already have a SR540 EXP all you need os to configure the dip switches properly. Have you tried to set the SR50 4EXP switches like this ?

You mist select Priority On for the priority feature to work on the DHW zone. You should also select the Priority protection. Just in case you have a stuck thermostat on your indirect water tank. You do not want the house to freeze up because the DHW thermostat didn't let the CH circulators to operate overnight

And of course you have the ZC low limit switch to on. That may need to be switched off depending on how the Boiler Circulator is electrically connected to the boiler wiring. More info needed on that switch option. Try on first then try off if you still have a problem.

Bbktrades

I discovered polarity of the 120v supply is a thing... Works now.