DIN-rail ESPHome OpenTherm gateway connecting OpenTherm-compatible boilers to Home Assistant. Provides full bi-directional control of setpoint, modulation level, DHW temperature, hot water demand and reads boiler diagnostics (flame, fault codes, return temp, modulation). Ships with ESPHome pre-installed. Integrates with Home Assistant climate entity for smart heating control with hybrid sources like wood fireplaces, solar collectors, and gas boilers.