Oven displays E4 and will not start, cooling fan may run continuously.

Safety first: Allow the oven to cool completely and disconnect power before working near thermostats or fans.

• Check ventilation: Ensure the Tristar oven has proper clearance around cabinetry and that front and rear vents are not blocked by panels or debris.
• Inspect cooling fan: Remove the top cover to access the cooling fan assembly. Spin the fan blades by hand; they should move freely. If stiff or seized, replace the cooling fan motor.
• Test overheat thermostat: Locate the high-limit thermostat (usually clipped to the top of the oven cavity or rear panel). With power off, disconnect its wires and test continuity. An open thermostat at room temperature indicates it has tripped or failed.
• Reset or replace thermostat: Some Tristar thermostats have a manual reset button; press it firmly if present. If no reset or it remains open, replace the cavity overheat thermostat with the correct Tristar-rated part.

After restoring power, run the oven at a moderate temperature and verify that the cooling fan operates and E4 does not reappear. Persistent E4 may indicate a faulty main control board temperature monitoring circuit.