Installing using relay control

The Passiv Smart Thermostat can be installed using either Modbus RS485 control or via relay control, similar to a standard smart thermostat. 

You can find a list of differences between the two control types here: Differences between Modbus RS485 control and Relay control

Installing the Passiv Smart Thermostat

For an in-depth installation guide, see Passiv Smart Thermostat Installation Guide. This article will go through relay-specific instillation steps.

1. Fit the Passiv Hub and Passiv Programmer as per the Installation Guide
   
   Fitting these two components is no different between a relay and RS485 installation.
    
2. Connect the Passiv Hub and the Passiv Programmer using RS485 cable
   
   Connecting the Passiv Hub and Passiv Programmer still uses RS485 Modbus. This is the only RS485 connection used in a relay installation. The RS485 connection on the Hub can be found on the back of the device. The RS485 connection on the Programmer can be found in the right set of connection in the wiring centre.
    
3. If necessary, connect Thermostats and zone valves to the Programmer
   
   If using Wired Thermostat, these connect into the bottom of the Programmer wiring centre. If using zone valves, these connect into the middle of the Programmer wiring centre.
    
4. Connect relay cabling into the 'Voltfree 1' set of connections
   
   There are three connections to use when connecting the heat pump to the Programmer via relay. These are labelled 'NC1', 'COM1' and 'NO1'. You can find a full diagram of the Programmer wiring centre here.
    
5. Connect other end of relay cabling as per manufacturer instructions
   
   Connect the other end of the relay cable you have just connected to the Programmer to either the indoor or outdoor unit of the heat pump (model dependent). Full instructions can be found in the manufacturer's guide for the heat pump you are installing.
    
6. Check that call for heat is working
   
   When there is a call for heat, the Passiv Smart Thermostat sends a relay 'ON' signal to the heat pump. You can check that this signal is being successfully sent and received using the in-home controls.