Connecting the Gateway to the boiler

Connecting a Gateway to the boiler varies slightly between Gateway editions. There is a difference between the latest Gateway Premium II and all other Gateways.

Gateway connectors

Each Gateway has the same three connectors:

(left to right)

  • EMS bus screw terminal
  • 3,5mm EMS service jack connector
  • JST connector
EMS Bus Gateway on boiler

Connecting a Premium II

Main method - 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. This is usually located on the front. Then stick the gateway to the metal side of the boiler. The underside of the case is magnetic. 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.

Alternative method - 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.

To use the screw terminal remove the top of the case to access the screw terminal by unscrewing the four case screws on the bottom. After you have connected the EMS bus wires and are sure it works properly you can screw the case top back again. 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.

Power source selection

The Gateway Premium II can be powered via the service jack or the EMS bus itself. To switch between power sources you need to move the buck voltage regulator to a certain position on the header. When the Gateway is delivered to you, the buck is mounted on the (lower) service jack power header position. To make use of bus power instead, move the buck to the (upper) EMS bus power header position. When you are using the jack plug to connect the Gateway, but the buck is on the EMS bus power header position, the Gateway will still draw its power from the EMS bus.

Gateway power source selector Gateway power source selector

Power considerations

The service jack on the boiler can provide more than enough power for the Gateway. The EMS bus itself however is limited in power. If you already have 2 or more devices (like thermostats, mixers) on the same EMS bus, there might not be enough power left for the Gateway. In case f.i. the thermostat doesn’t function properly after connecting the Gateway, you need to connect the Gateway via the service jack or use an external USB adapter (see below).

First boot -> Check the LED

If you plug the gateway into the boiler, the on-board LED of the Wemos will start blinking fast for the first few seconds. Then it will start to blink slow as a sign its looking for the EMS bus. As soons as it has discovered the EMS bus, it will light up solid. If the Gateway has already been configured before, the LED will light up solid really quickly after boot.

If it lights up solid, then go to Connecting the Gateway to your home network. If you don’t see any LED or it keeps blinking, go to Troubleshooting.

Connecting to the boiler (all other Gateways)

Main method - service jack

With the supplied jack cable you can plug in the gateway to the service jack of the boiler. This is usually located on the front. Then stick the gateway to the metal side of the boiler. The underside of the case is magnetic. The entire device including the Wemos is powered via this service jack. So no additional power supply needed. Just the jack cable is all you need. It’s important that you first plug in the cable to the gateway and then into the boiler. Otherwise you momentarily shortcut the bus when inserting the cable into the jack of the gateway.

Alternative method - 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. In this case you can’t use the buck voltage converter. You need to power the device by plugging in a USB power supply directly to the Wemos.

If you have a Premium Gateway with a Lolin Wemos V3, you need to remove the plastic tabs on the bottom side of the Wemos so the USB connector of the Wemos will be accessible from the side with the top case attached. If you have a Gateway Regular, the USB connector on the Wemos V2 is already accessible. So you don’t have to remove the tabs.

Wemos mod

First boot -> Check the LED

If you plug the gateway into the boiler, the on-board LED of the Wemos will start blinking fast for the first few seconds. Then it will start to blink slow as a sign its looking for the EMS bus. As soons as it has discovered the EMS bus, it will light up solid. If the Gateway has already been configured before, the LED will light up solid really quickly after boot.

If it lights up solid, then go to Connecting the Gateway to your home network. If you don’t see any LED or it keeps blinking, go to Troubleshooting.