Why would opentherm bridge only work when connected via an opentherm gateway.

Hi,

Just wondering if anyone could suggest why connecting a honeywell opentherm bridge directly to my boiler doesn't work, but works fine when it is connect via an opentherm gateway.

the gateway is just one of these.
https://diyless.com/product/esp8266-opentherm-gateway

so only extra power is the usb connected to the d1 mini,