Safety first: Disconnect the oven from mains power before removing any panels. Beware of sharp metal edges.

Steps to check:

Ventilation check: Ensure the oven's top and rear vents are not blocked by cabinetry, insulation, or stored items.
Access cooling fan: Remove the top or rear cover (depending on model) to access the cooling fan assembly.
Spin test: Try spinning the fan blades by hand (with power off). If stiff or seized, the fan motor is likely faulty and must be replaced.
Power test: With a multimeter and extreme caution, verify that the fan receives mains voltage when the oven is heating (this should be done only by someone competent with live testing).
Check overheat thermostat: Locate the safety thermostat (usually clipped to the top of the oven cavity). Test for continuity. If open and non-resettable, replace it. Some models have a manual reset button—press it if present.
Replace faulty parts: Fit a new cooling fan motor or thermostat as required, ensuring all wiring is reconnected securely.

E4 error code, oven fan runs but heating is disabled.

Possible Causes