The display shows E03, indicating an overheat or high limit trip on the Riello furnace.

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

Blower fan not running, Blocked air filter or ducts, Faulty high limit switch, Oversized firing rate for the furnace

Safety: Turn off power and allow the furnace to cool. Do not bypass the high limit.

Steps:

Reset high limit: If manual reset, press the button once after cooling.
Check airflow: Replace dirty filters, open closed registers, and verify blower operation.
Inspect blower motor: Listen for humming or overheating. Replace a failing motor or capacitor.

If E03 recurs, have a technician verify the firing rate and heat exchanger condition.

Hard 4/5

High Limit Thermostat

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