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Brass auto-fill valve with pressure gauge, half-inch FNPT threads

Legend Valve

Legend Valve 800-842 1/2" AF-480 Auto Fill with Gauge accessory

SKU CH-NY69-AT6S3

Auto-fill valve with integrated gauge maintains boiler pressure automatically

  • Auto-fill valve maintains system pressure automatically
  • Built-in gauge shows pressure at a glance
  • 1/2" FNPT connection fits standard piping
  • Legend Valve 800-842 model for reliable performance
  • California Prop 65 listed for chemical awareness

Auto-fill valve for hydronic systems

The Legend Valve 800-842 is a 1/2 inch auto-fill assembly with an integrated gauge. It automatically maintains water pressure in closed-loop hydronic heating installations. The unit connects via FNPT threads and carries a California Proposition 65 warning for chemicals linked to cancer and reproductive harm.

Suits installers needing automatic make-up water

This accessory fits contractors who want a single component that combines fill regulation and pressure indication. It is not for installers who prefer a separate backflow preventer and pressure gauge, nor for systems that require a different connection type than FNPT.

Verify compatibility before ordering

Confirm that the existing boiler or radiator circuit uses a 1/2 inch FNPT connection for the auto-fill point. Check that the system pressure range matches the gauge scale on this model. Ensure local codes accept an integrated auto-fill device without additional backflow protection.

How it compares

Measured against everything we stock in Radiator Fans & Boiler Parts, at today’s prices. Recalculated every night.

Price $74.99
Pricier than about 82% of the 95 comparable items (median $25.99).

Specifications

Product
Brand nameLEGEND VALVE

Questions about this item

What size piping is required to connect the 1/2" AF-480 auto fill valve?

The valve uses a 1/2 inch female NPT connection, so you need matching 1/2 inch male NPT piping or fittings for installation.

Will the 800-842 auto fill valve operate correctly with an older boiler system?

Yes, the 1/2 inch FNPT connection is a standard interface compatible with many existing hydronic heating systems and older boiler piping.

How can I verify the Legend Valve 800-842 is maintaining pressure after installation?

Observe the integrated gauge needle; it should display a stable pressure reading that matches your system's required fill pressure setting.

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