Honeywell Gas valve VK8515MR4571U

The Honeywell VK8515MR4571U is a gas valve from the VK series, designed to shut off and meter gas supply to a burner. It opens on command from the burner control only when the gas pressure switch permits, and in premix boilers, a pneumatic gas/air link ties the valve to the fan. This valve is a critical component in the fuel admission step of the ignition sequence, where after pre-purge and spark, the burner control energises the valve coil to allow gas flow and flame proving.

When selecting a replacement gas valve of this type, verify three parameters: connection size (typically Rp 1/2" to 2" or flanged), coil voltage (230 V or 24 V AC/DC), and function type (single or double solenoid, slow opening, servo-regulated, multiblock with integrated filter and regulator). Ensure the valve's orientation and mounting match the original installation to avoid stress on the pipework. The coil is often replaceable separately from the valve body, which may allow a lower-cost repair if the valve body is sound.

Common failure modes for valves of this class include coil burnout, leaking seat, drifting outlet pressure, and a seized servo regulator. When these occur, the burner may fail to ignite, experience unstable flame, or shut down unexpectedly. Check the coil continuity, valve seat sealing, outlet pressure stability, and servo regulator movement.