What is a welded contactor alarm?

Each HZ-ICE zone is switched by a definite-purpose contactor. A welded contactor is one that has failed in the closed (on) position — it continues passing current even when the panel has commanded it off. HZ-ICE detects this condition by monitoring current in a zone that should be off: if current is flowing when the panel has not commanded that zone to heat, a welded contactor alarm is generated. This is a safety-critical fault — the affected zone should be disabled from the dashboard and service called immediately.