Miller furnace digital display shows E4; blower may run without heat.

This repair may involve working with high voltage components or water connections. Always unplug the appliance before removing any panels.

If you are not confident in your ability to perform this repair safely, we strongly recommend contacting a professional technician.

Possible Causes

Chronic overheating from restricted airflow, Failed blower motor, Faulty limit switch stuck open, Oversized furnace for duct system

Safety: Allow the furnace to cool and turn off power before testing limits.

Correct airflow issues: Replace filters, open registers, and repair duct restrictions.
Test blower motor and capacitor: Verify proper amperage draw and capacitor value. Replace weak components.
Replace faulty limit: If the main limit remains open when cool, replace it with the correct Miller-rated temperature limit.
Professional evaluation: If overheating persists, have a technician evaluate duct sizing and furnace capacity.

Hard 4/5

High Limit Switch

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