Error code reference

Lennox Furnace Error Code 4 Flashes (RAM)

Open limit

Open limit — primary limit, rollout switches, or secondary limits open.

First step from the service manual

Check primary limit, rollout switches and secondary limits; find source of overtemperature; reset or replace limits as necessary.

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

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Step-by-step tests with expected resistance, voltage, and continuity values
Wiring diagram references and connector pinouts from the OEM service manual
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4 Flashes (RAM) on my Lennox Furnace

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Open limit — primary limit, rollout switches

From Service Manual 321401, p.13:

1.Check primary limit, rollout switches and secondary limits; find source of overtemperature; reset or replace limits as necessary.

2.Measure control board supply voltage at the test points. Expected: 12 VDC and 5 VDC; a drop below 4.75 VDC on the logic rail points to a failed onboard regulator.

3.Inspect all connectors on the main control for corrosion, thermal stress, or backed-out pins. Reseat each connector with the power disconnected.

Part WPW10804018

Electronic control board

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First step from the service manual

Get the full diagnostic procedure for 4 Flashes (RAM).

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