The Honeywell Home 40003916-026/U is a 24VAC replacement power head with an integrated SPST end switch, purpose-built to restore full automatic operation to V8043E series zone valves in hydronic heating systems. Rated for 50/60Hz and a maximum ambient temperature of 125°F, this actuator mounts directly to an existing V8043E valve body — no pipe work, no draining, no system shutdown. For residential and light commercial boiler systems running multi-zone hot water distribution, it is the factory-matched solution when the original actuator wears out. Why the Power Head — Not the Whole Valve — Is Usually the Right Fix When a V8043E zone valve stops opening or fails to signal the boiler, the valve body itself is rarely the problem. The brass valve seat and ball mechanism inside these Honeywell zone valves are built to last decades. What typically fails first is the actuator motor — the electrical and mechanical head sitting on top of the valve body. Replacing only the 40003916-026/U power head restores complete system function at a fraction of the cost of pulling and re-soldering an entire valve assembly. This repair-without-disruption design is one of the defining characteristics of the V8043E platform. The 40003916-026/U unclips from the valve body while the system is still full of water. No torches, no drain valves, no waiting for the system to cool down below operating pressure. For a heating contractor working through a cold-weather callback, that distinction matters enormously. Exact Compatibility: Which V8043E Models Accept the 40003916-026/U The 40003916-026/U is the correct replacement head for V8043E series zone valves that were originally equipped with an end switch. Confirmed compatible valve body models include the V8043E1012, V8043E1061, V8043E1079, and V8043E1020. All of these share the same actuator mounting interface and the same four-wire electrical configuration the 40003916-026/U is built around. It is worth noting that V8043A and V8043F valve bodies have different power head designs. Before ordering, verify the full model number printed on the existing valve body. If the valve label shows V8043E followed by any four-digit suffix, the 40003916-026/U is the correct actuator replacement, provided the original head carried an end switch. A V8043E without an end switch uses a different head and a different wiring configuration. What the SPST End Switch Actually Does in a Multi-Zone System The end switch is the feature that separates the 40003916-026/U from simpler two-wire actuator replacements, and understanding it is essential for correct installation. When the thermostat in a given zone calls for heat, 24VAC energizes the yellow motor leads on the valve head. The synchronous actuator motor drives the valve from its normally-closed position to fully open — a mechanical process that takes a few seconds. Only once the valve is truly open does the internal SPST end switch close. That switch closure, carried on the two red leads, is what signals the boiler to fire and the circulator pump to run. This sequencing prevents the boiler from firing into a closed hydronic loop. In a multi-zone system with three or four V8043E valves, the end switches from each valve are typically wired in parallel to the aquastat or relay panel. The boiler only receives a call to fire when at least one zone valve has confirmed it is open. The 40003916-026/U's end switch is rated for 50 VA pilot duty at 24V and 4.4 amperes running at 120V, which comfortably covers direct relay coil switching and pump starter loads
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