What E303 Means
E303 watches the rate of change rather than the absolute figure. The sensor on the control module has seen the board's temperature climbing faster over time than Bosch allows, so heating stops and the cooling fan goes to high speed. As with the absolute over-temperature code, heating resumes at 212 degrees Fahrenheit and self-clean stays disabled until a control reset is performed.
Common Causes of E303
- Cooling fan failing or running below speed
- Ventilation path above or below the door restricted
- Relay stuck closed, adding heat the control did not ask for
🔧 One Safe Check You Can Try
Listen for the cooling fan while the oven is warm. A fan that never starts, or one that sounds slower and rougher than it used to, matches the first thing Bosch asks technicians to establish here.
⚠ Why You Shouldn't Go Further Than That
- A rate-of-rise fault usually means cooling has degraded rather than stopped, which is harder to spot than a fan that has simply died.
- Bosch's list includes a stuck relay, so an element may be energised independently of the front panel.
- The fan and the module share the plenum above the cavity, and that space runs hot for a long time after cooking.
- Replacing a fan that was actually fine because the real issue was a blocked trim leaves the oven doing the same thing with a new part in it.
Opening a panel to inspect or repair something yourself doesn't automatically cancel your manufacturer's warranty — but it can risk accidental damage, and some manufacturers do have specific service conditions. Check your product's warranty terms, or ask us, before deciding.