The Hayward® HDXFDPS400 is a Differential Pressure Switch for Hayward's HDF400 Heater. The industry’s smallest footprint heater allows replacement of almost any heater in an existing pad with the efficient reliability of the new Universal HC Series dual-fuel technology heater from Hayward®. Built to fit effortlessly with Hayward plumbing adapters, every detail has been thoughtfully engineered with easy drop-in capability in mind—its dual-fuel technology, its adaptive plumbing, its zero wall-clearance design, and more. And it all adds up to a durable, ultra-powerful heater with the industry’s smallest footprint.