Package Deal: Azel SP-85 with 5 units of D-135E Digital Thermostats for Radiant Floor Heating * Isolated End Switch and Priority End Switch * Addition features for SP-84/85/86: Manual priority override(bypass) for each of the secondary zone * Priority timer for protection of a priority zone malfunction and prevention of freeze-ups in the heating zones. * Capable of turning on extra system circulator * Unlimited zone expansion