trying to control 433MHz wireless thermostat with Arduino


I have the following wireless thermostat:

The AC819 transceiver has a relay which turns the boiler on/off when it receives a 433MHz signal from the wireless timer unit. And I'm trying to wire the Arduino to this relay.

The objective is to use Arduino to switch the relay (to turn boiler on/off) .. in parallel with the wireless timer. So, the existing wireless timer should continue to work as normal, but the Arduino can 'override' by turning boiler on/off.

Can anyone help with the wiring? I'm guessing that I connect two arduino pins to the input of the relay. Not sure if I need a transistor circuit in between..?

Any help or suggestions would be much appreciated.

Thanks. Best regards,