Zone 2 Works Without Pump, Fails With Pump – Relay Interference

Zone 2 runs in test mode (no pump), but fails when pump starts. Pump has relay on controller.

Diagnosis

Disconnect pump start wire at controller.
Run zone 2 manually; measure voltage at zone 2 terminal (should be 22–26 VAC).
Reconnect pump wire; measure again. Voltage drop = short in pump wire or controller.
If voltage OK, valve diaphragm may fail under higher pressure.

Rebuild or replace valve.

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