Bosch HGI8054UC Error Code E303

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• Source: Official Bosch service manual
• Reviewed by: Geo Technical Editorial
• Published: March 1, 2026
• Updated: March 15, 2026
• DIY scope: Basic user checks are possible.

Error E303 on Bosch : Relay module overtemperature — oven cavity temperature repeatedly exceeded maxim. Follow the troubleshooting steps below to diagnose and fix this range issue. ## What Error Code E303 Means on a Bosch HGI8054UC Relay module overtemperature — oven cavity temperature repeatedly exceeded maximum safe threshold at the relay module ## What This Error Means Error code E303 on your Bosch 800 Series Slide-In Range means the oven’s relay module has recorded excessive internal temperature over a cumulative period. Unlike E115 (immediate overtemperature event), E303 typically indicates a systemic cooling problem — the oven interior has been running hotter than normal over multiple cooking cycles, stressing the relay module. Root causes include: a cooling fan running at reduced efficiency, clogged oven bottom vent slots preventing hot air from escaping properly, a stuck bake or broil relay keeping a heating element or igniter slightly energized during cool-down, or a deteriorated door gasket allowing oven heat to radiate into the control area. On gas models, E303 can also be caused by an igniter that continues to glow after the gas valve closes, adding heat to the oven cavity during the off-cycle. Igniter resistance for Bosch gas ranges should be approximately 40–96 ohms when cold — an igniter below 25 ohms draws excessive current and may not fully extinguish. ## Quick Diagnostic Summary | Detail | Value | |--------|-------| | Error Code | E303 | | Severity | High | | Appliance | Bosch HGI8054UC 800 Series Gas Slide-In Range | | User-Fixable | Yes | | Applicable Models | HEI8054U, HGI8054UC, HDI8054U | ## Step-by-Step Troubleshooting | Step | Action | What To Do | Expected Result | |------|--------|------------|-----------------| | 1 | Power off and inspect oven bottom vent slots | Turn off the range at the circuit breaker and allow it to cool fully. Remove the oven bottom panel (typically lifts out after two front screws). Inspect the vent slots along the rear and sides of the oven floor for baked-on grease, debris, or foil. Clean all vent slots thoroughly with a non-abrasive cleaner. | All oven floor vent slots are clean and unobstructed. Bottom panel is reinstalled. | | 2 | Inspect the door gasket seal | Close the oven door on a sheet of paper at multiple points around the gasket perimeter. The paper should resist being pulled out at all points. A loose or deteriorated gasket allows oven heat to escape into the control cavity, raising relay module temperatures over time. | Door gasket grips paper firmly at all points around the perimeter. No gaps detected. | | 3 | Test cooling fan at full speed | Restore power. Enter Service Mode (hold Clock + + for 5 seconds until ‘tESt’). Navigate to FAnS (fan test) and run the fan at full speed. The fan should run audibly at high speed. Also observe the fan speed variation during a bake cycle — the fan should ramp up as the oven heats and ramp down after it is turned off. | Cooling fan reaches full speed in fan test. Fan runs variably during bake cycle. | | 4 | Test igniter resistance (gas models only) | Power off the range and shut off the gas supply. Remove the oven bottom panel and burner cover. Locate the bake igniter (glowing rod near the burner). Disconnect the igniter harness connector. Measure resistance with a multimeter. Normal range: 40–96 ohms. Below 25 ohms = excessively low resistance causing the igniter to glow during off-cycles, adding heat to the oven cavity. | Bake igniter reads 40–96 ohms (normal range). An igniter reading below 25 ohms should be replaced. | | 5 | Replace control board if all components test good | If the oven vents, door gasket, cooling fan, and igniter (if gas) all test within spec but E303 persists, the relay module’s internal thermal monitoring has drifted or a relay is marginally stuck. Replace the control board. After installation, run 3 consecutive bake cycles at 375°F for 20 minutes each to confirm E303 does not return. | Three consecutive bake cycles complete without E303. Oven temperature is stable and heating cycles normally. | ## Frequently Asked Questions ### Why does E303 appear after years of normal use with no changes? Over time, cooling fan bearings wear and reduce airflow slightly, oven vent slots accumulate grease reducing heat escape, and door gaskets compress reducing their seal effectiveness. Each factor alone might not trigger E303, but together they reduce the thermal margin enough that E303 appears. Cleaning vents, checking the gasket, and confirming the fan runs at full speed often resolves E303 on older ranges. ### E303 on a gas range — should I check the igniter? Yes — on Bosch gas slide-in ranges, a weakening igniter (one with resistance below ~25 ohms) can stay at a low glow during the off-cycle, continuously adding heat to the oven cavity. This is a common cause of E303 on gas models that passes unnoticed during normal operation because the igniter still lights the burner correctly. ### Can I prevent E303 with regular maintenance? Yes. Clean oven floor vent slots every 3 months by removing the bottom panel and wiping the slots. Check the door gasket annually with the paper-slip test. Ensure the range has proper installation clearances. These maintenance steps keep thermal margins healthy and reduce the risk of E303 appearing. ### Is E303 the same as E302? No. E302 = control board electronics overtemperature (board’s own internal sensor exceeded ~212°F). E303 = relay module overtemperature (the relay section of the board recorded excessive heat from the oven cavity side). E302 is more urgent; E303 indicates a slower thermal buildup. Both should be investigated promptly. --- Last Updated: March 2026 · Bosch 800 Series Gas Slide-In Range · Error Code E303 ### Is it safe to keep using my Bosch with error E303? If error E303 does not indicate an immediate safety hazard such as a gas leak, electrical short, or water flooding, you can continue limited use while monitoring the appliance. However, running the range with an active error code increases the risk of further damage. Address the underlying issue as soon as possible. For high-severity errors, disconnect the appliance and contact a qualified technician. ### How much does it cost to fix error E303 on a Bosch ? Repair costs for error E303 on the Bosch range depend on the root cause. DIY fixes such as cleaning filters, resetting the unit, or reconnecting loose wires cost nothing beyond basic tools. If a component replacement is needed, parts and labor from a certified technician are the main expenses. Contact a Bosch-authorized service provider for an accurate estimate based on your specific situation. ### What does error code E303 mean on a Bosch range? Error code E303 on Bosch range models indicates Relay module overtemperature — oven cavity temperature repeatedly exceeded maximum safe threshold at. This error is detected by the appliance’s internal diagnostic system and displayed to alert the user that attention is needed. Refer to the troubleshooting steps above for guidance on resolving this issue. ### Is it safe to keep using my Bosch with error E303? If error E303 does not indicate an immediate safety hazard such as a gas leak, electrical short, or water flooding, you can continue limited use while monitoring the appliance. However, running the range with an active error code increases the risk of further damage. Address the underlying issue as soon as possible. For high-severity errors, disconnect the appliance and contact a qualified technician. ### How much does it cost to fix error E303 on a Bosch ? Repair costs for error E303 on the Bosch range depend on the root cause. DIY fixes such as cleaning filters, resetting the unit, or reconnecting loose wires cost nothing beyond basic tools. If a component replacement is needed, parts and labor from a certified technician are the main expenses. Contact a Bosch-authorized service provider for an accurate estimate based on your specific situation. ### What does error code E303 mean on a Bosch range? Error code E303 on Bosch range models indicates Relay module overtemperature — oven cavity temperature repeatedly exceeded maximum safe threshold at. This error is detected by the appliance’s internal diagnostic system and displayed to alert the user that attention is needed. Refer to the troubleshooting steps above for guidance on resolving this issue.