Error code reference

Lennox Furnace Error Code 3+1

Limit switch open (primary or secondary).

First step from the service manual

Check continuity across limit switch(es); switches reset automatically upon cool down. Check for restrictions on blower inlet and outlet air.

The complete diagnostic procedure includes additional test steps, resistance specifications, wiring diagram references, and component test points.

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Limit switch open (primary or secondary)

From Service Manual 680133, p.25:

1.Check continuity across limit switch(es); switches reset automatically upon cool down. Check for restrictions on blower inlet and outlet air.

2.Measure the inlet valve coil resistance at the valve connector. Expected: 1,000 to 1,200 ohms per coil at room temperature.

3.Verify static water supply pressure at the inlet hose. Below 20 psi or fluctuating supply commonly triggers fill-timeout faults.

Part WPW10212598

Water inlet valve

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