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This is the diagram of the wiring of my boiler when the circuit is closed and it is heating the water in the hot water cylinder.



In my boiler, I have three contacts Tc, TB1, and TB2 as shown in the picture.

Which is supposed to be the correct wiring in the BDR91?

Since according to the Honeywell diagrams, the wiring in the BDR91 is made connecting wires only to A and B leaving C not connected and used when the circuit is closed. But what about when I have three wires?

The connection I would make would be the following

BDR91 | Boiler
A Tc
B TB1
C TB2

In this way when the circuit is closed A and B are closed and the BDR91 is active. otherwise the circuit is opened

Yes, if you have a Motor Open / Motor Closed zone valve, you would need to use the C contact.

Thanks a lot. it worked.