Oven heats but does not reach set temperature or takes excessively long to preheat.

Safety first: Turn off power before testing elements or sensors.

• Step 1 – Verify with thermometer: Place an oven-safe thermometer in the center of the oven and preheat to 350°F (175°C). Compare the displayed temperature to the thermometer after 20–30 minutes.
• Step 2 – Inspect door gasket: Check the door seal all around for gaps, tears, or hardened sections. Replace the gasket if it does not seal evenly.
• Step 3 – Check bake element: Observe the bake element during preheat; it should glow red uniformly. Dark spots or uneven glow indicate a failing element. Test resistance and replace if out of spec.
• Step 4 – Test temperature sensor: With power OFF, measure resistance of the sensor at room temperature and compare to Zline specs. Replace if out of range.
• Step 5 – Adjust calibration (if available): Some Zline controls allow temperature offset adjustment in the settings menu. If the oven is consistently off by a small amount (e.g., 10–30°F), adjust the calibration per the user manual.

Note: Large temperature errors usually indicate a hardware fault rather than calibration.