OSC21 Optimizer with an outside and a room sensor. Replacement RVL480 is a compensator / optimiser with additional functions, and the same dimensions. The existing room and outside sensors can be re-used. If no control of the flow temperature is needed, the flow temperature sensor can be simulated by a fixed 1300 ohm resistor (63°C) across terminals B1 and M. (
Info: If the OSC21 is used together with an RVLxx heating controller, both can be replaced by the RVL480 device).