Connecting a Gateway S32 (ESP32 Standard edition)

Gateway connectors

The Gateway S32 has four connectors:

  • EMS bus screw terminal

  • 3,5mm EMS service jack connector

  • DC barrel jack connector (5.5/2.1mm)

  • JST connector (3-pin JST 1.5mm ZH)

EMS Bus Gateway S32 connectors

Preferred order of connection

In short this is the best order in which you should try to connect the Gateway:

  • Service jack (If your boiler has one).

  • If you have a solar or mixer module with a bus OUT: EMS bus wires on EMS OUT terminal of the module.

  • If you don’t have an external module use the same EMS bus terminal as to which the thermostat is connected or should be connected to.

The service jack provides enough power for the Gateway. In case you use the screw terminal also plug in the DC adapter. You do not need to use the DC adapter when you are using the service jack cable.

Service jack

EMS Bus Gateway on boiler

With the supplied jack cable you can plug in the Gateway to the service jack of the boiler. The entire device is powered via this service jack. So no additional power supply needed. Just the jack cable is all you need. First plug in the cable to the Gateway and then into the boiler. If the Gateway is plugged in, it will start blinking slowly to indicate it’s working and looking for the EMS bus and WiFi network.


If you plug in or unplug the jack cable from the Gateway first instead of the boiler side, you may momentarily shortcut the boiler. It will then reboot, which can cause some clicking noises. Nothing to worry about but just unplug the boiler side first.

EMS/thermostat wires

If your boiler does not have a service jack or it does but you want to mount the EMS Bus Gateway elsewhere you can use the screw terminal to connect to the two EMS bus wires. This can be in parallel with the thermostat or from inside the boiler. You have to use the DC adapter when you are using the screw terminal.

The Gateway has a green external screw terminal.

Gateway screw connector

On almost all boilers it does not matter which EMS wire you connect to which of thse two terminal pins, as the Gateway has an internal correction circuit. However a few boilers and f.i. if you have an RC310 installed the orientation does matter. If installed the wrong way, the display of the boiler will not show anything. If this is the case, just switch both EMS wires on the Gateway.

You can see here how to locate the correct EMS bus terminals on your boiler: Connecting the Gateway to the boiler side.

If the Gateway is connected correctly, it will start blinking slowly to indicate it’s working and looking for the EMS bus and WiFi network.

Do not connect both the jack and the screw terminal at the same time. Both connectors are internally hardwired so by connecting both at the same time you can short circuit the bus.

First boot -> Check the LED

If you plug the Gateway into the boiler or you connect the power plug, the red on-board LED will light up solid and the blue LED will start to blink slow as a sign it has booted and looking for the EMS bus. As soons as it has discovered the EMS bus and your Wi-Fi network, it will light up solid. If the Gateway has already been configured before, the LED will light up solid really quickly after boot. But if it’s new and not connected to your WiFi network yet, it will continue to blink slowly.

The blink speed can be compared at this Youtube video of Gateway LED blink speed 1.

If the light is blinking slowly, then go to Connecting the Gateway to your home network. If you don’t see any LED go to Troubleshooting.