The Chill depends on your heating system's configuration. The system may be unbalanced, meaning too much or too little water is reaching the Chill. As a result, the water heated by the Chill recirculates instead of reaching the hybrid (where the heat is dumped outside).
If a radiator is warming up, close that radiator's valve. This helps keep water circulating through the whole system.
If the Chill is in a series configuration and that radiator is warming up, it's important to keep that valve open — but you can close other radiators to improve circulation in the system.